1. At the top of the forum, there are round buttons, click on the yellow-ish gold one that says "Profile"
2. On that page you can modify your user name, gender, location, age, links etc
3. If you look closer there are smaller links in black that line the top of that page (above the info edit box, but below the large colored buttons).
Information | Preferences | Signature | Avatar | Friends and foes | Topic(s) being watched | Favourites
You can change all of those things by clicking on each link!