problems with bwareaopen in segmenting

hello, I am using bwareaopen to remove a part of the image i dont want. Here is my code

a=imread('C:\Users\S\Desktop\project\A data\figure10.jpg');
a=im2bw(a);
az=bwareaopen(a,500);
imshow(az);

But i have been unsuccessful. If anyone can help me with this, I will be greateful. Thank you

This is my input image:

Thank you.