Click that big grey "profile" button, right below that "total time logged in:" message. From there, on the left side of the screen, click "Forum Profile Information".
You'll see a couple of fields there. One of them says "I have my own pic". You can paste the link of a picture there and set it up as your avatar/display pic/profile picture. It has to be tiny. Paste it there, then click "Change profile", right on the bottom right side of the screen.
A nice place to upload pictures is
www.imgur.com