Sorry about this, the system is confusing because we can't figure out yet how to keep you logged in to both the forum and the main site, and you need to do it on the main site. So if you just click 'Profile' from the forum you'll still have to log in to the other site, annoyingly
Anyway, here's how to do it.
1. First, go here:
2. Then type your name and password in the boxes in the TOP RIGHT of the screen and click 'Log In'.
3. Then when screen reloads saying "Welcome [your name]" click "Edit Profile".
4. You can upload or change your avatar on this edit profile screen.
Hope to see some more faces about here soon