To upload an avatar you must first click the 'profile' button on the red navigation bar.
After you have done that there should be an 'avatar' link just under the red navigational bar. Click it.
If you have an avatar already you must click 'choose' next to the 'Upload an avatar from your computer' box.
Then just navigate around your documents and double click on the picture you want as your avatar.
After you have done that, click 'save' at the bottom of the screen.
Hope this helped!