#1 Click on "settings" at the top right in blue.
#2 Under my settings in the left hand column click on "Edit Avatar"
#3 A box like this will appear, check the "use costume avatar" button.
#4 make sure you click on "save changes" at the bottom of the page. Also note the size limitations of the avatar you can insert. If you have a picture that can be resized send me a private message and I'll re-size it for you.