Click on your Avatar in the right side of the banner.
Hover over the Avatar and it will say EDIT AVATAR, click on it.
"Drag this image to crop it, then click Okay to confirm, or upload a new avatar below."
Depending on the size and shape of your picture you may be able to show the top of your head.
I repositioned mine but it's too wide so I only get the left or right side of the picture.