Can not connect to serial port my MATLAB-arduino comunication

Hi, i'm doing a project:

------------------------ ''Only the serial communication zone needs to be solved ''

% --- Executes on button press in iniciar.

function iniciar_Callback(hObject, eventdata, handles)

% hObject handle to iniciar (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%% NOOOOOOOO close all;

clc;

y=zeros(1,1000); %Vector on es guardaran les dades

pressio = 0;

pressio_ini = pressio_inicial(); %pressio inicial a la superficie

%%%% provaaaaaa pressio_ini = 200;

%Mostrem la pressió inicial ACTUAL a la superficie terrestre

fprintf('Pressió inicial actual a la superfície terrestre: %.2fkPa\n', pressio_ini);

%Inicialització port sèrie

delete(instrfind({'Port'},{'COM7'}));

serialPort = serial('COM7');

serialPort.BaudRate=9600;

warning('off','MATLAB:serial:fscanf:unsuccessfulRead');

%Creació i obertura arxiu resultats.txt

fid=fopen('resultats.txt','w');

%Obrim el port

fopen(serialPort);

%Enviem S a Arduino

fprintf(serialPort,'%s\n','S');

%pause(1);

%fprintf(serialPort,'%s\n','o');

%Declaram un comptador del nombre de mostres ja preses

i=1;

%Crem finestra per a la gràfica

%%%% NOOOOOOOOOOOOO figure('Name','Serial communication: Matlab + Arduino.')

title('SERIAL COMMUNICATION MATLAB+ARDUINO')

xlabel('Pressió cada 200ms')

ylabel('Metres sota aigua [m]');

grid on;

hold on;

%Descartem el primer valor (és text)

pressio=fscanf(serialPort,'%d');

global lletra teclatoboto mostres

lletra='p';

a='p';

mostres=9999; %Posem moltes mostres i, si premem el botó Aturar, posarem la mostres=1 perquè s'aturi.

%Bucle que llegeix i dibuixa les mostres

while(i<=mostres)

ylim([-1 5]);

xlim([i-20 i+5]);

pressio=fscanf(serialPort,'%d');

%y(i)=((pressio[bits]*(5[V_AO]/1023[bits])*(1[V_SENS]/161[V_AO])*(1[KPa]/0,2e-3[V_AO]))[pressio mesurada sensor KPa]-pressio_inicial[KPa]))*(10[m Aigua]/100[KPa]); %PASSEM ELS BITS A BAR I DE BAR A COL AIGUA NORMALITZADES

y(i)=((pressio*(5/1023)*(1/161)*(1/0.2e-3))-pressio_ini)*(10/100);

%y(i)=(pressio(1)*(1/pressio_inicial)*10)-10;

plot(i,y(i),'X-r');

drawnow

%Escrivim les dades a resultats.txt

z=[i;y(i)];

fprintf(fid,'%d %.3f \n', z);

hold on;

%Escrivim les dades a resultats.txt

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%Si indiquem que volem controlar per teclat, llegirem per teclat. Si

%indiquem que per botons, per botons.

if (strcmp(teclatoboto,'teclat'))

a=llegir_tecles3;

elseif (strcmp(teclatoboto,'boto'))

a=lletra;

pause(1);

end;

disp(a);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

fprintf(serialPort,'%s\n',a);

i = i + 1;

end

%Enviem o per tancar rele

%fprintf(serialPort,'%s\n','o');

%pause(20);

%Tancam la connexió amb el serial i l'arxiu

fclose(serialPort);

fclose(fid);

delete(serialPort);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% --- Executes on button press in teclat.

function teclat_Callback(hObject, eventdata, handles)

% hObject handle to teclat (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of teclat

global teclatoboto

teclatoboto='teclat';

% --- Executes on button press in botons.

function botons_Callback(hObject, eventdata, handles)

% hObject handle to botons (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of botons

global teclatoboto

teclatoboto='boto';

% --- Executes on button press in on.

function on_Callback(hObject, eventdata, handles)

% hObject handle to on (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of on

global lletra

lletra = 'm';

% --- Executes on button press in off.

function off_Callback(hObject, eventdata, handles)

% hObject handle to off (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of off

global lletra

lletra = 'n';

% --- Executes on button press in endavant.

function endavant_Callback(hObject, eventdata, handles)

% hObject handle to endavant (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of endavant

global lletra

lletra = 'w';

% --- Executes on button press in endarrere.

function endarrere_Callback(hObject, eventdata, handles)

% hObject handle to endarrere (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of endarrere

global lletra

lletra = 's';

% --- Executes on button press in dreta.

function dreta_Callback(hObject, eventdata, handles)

% hObject handle to dreta (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of dreta

global lletra

lletra = 'd';

% --- Executes on button press in esquerra.

function esquerra_Callback(hObject, eventdata, handles)

% hObject handle to esquerra (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of esquerra

global lletra

lletra = 'a';

% --- Executes on button press in pujar.

function pujar_Callback(hObject, eventdata, handles)

% hObject handle to pujar (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of pujar

global lletra

lletra = 'r';

% --- Executes on button press in baixar.

function baixar_Callback(hObject, eventdata, handles)

% hObject handle to baixar (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of baixar

global lletra

lletra = 'f';

% --- Executes on button press in radiobutton11.

function radiobutton11_Callback(hObject, eventdata, handles)

% hObject handle to radiobutton11 (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

% Hint: get(hObject,'Value') returns toggle state of radiobutton11

global lletra

lletra = 'p';

% --- Executes on button press in aturar.

function aturar_Callback(hObject, eventdata, handles)

% hObject handle to aturar (see GCBO)

% eventdata reserved - to be defined in a future version of MATLAB

% handles structure with handles and user data (see GUIDATA)

global mostres

mostres=1;

--------------------

and can run it( the guide) because when i press the initializate pushbotton it says me this error:

--------------------

Error using serial/fopen (line 72)

Open failed: Port: COM7 is not available. Available ports: COM1, COM3.

Use INSTRFIND to determine if other instrument objects are connected to the requested device.

-------------------

I'm using Matlab 2018b and don't know how to change the port used in this scretch. I tried to tip COM3 or 4 on scretch wich are avaliable in my Matlab but it still talks about COM 7!!.

Thanks :)