Step 1:
After you login successfully, click on the icon circled in red as shown in the image below.

Step2:
You will be taken to a page with a big blue button, click on it to choose your preferred pix, or click on the red button to remove the current pix before clicking on the blue button.

Step 3:
After getting the pix of your choice, crop it to get the area of the pix you need and save.