Click on Private Messages up on the right under your name OR on the task bar on the far left where it says My Profile.

My Profile FAQ/Help Members List Calendar New Posts Search Quick Links DailyMood Log Out

That takes you to your control panel.... on the left side is a column where you may edit your details, profile, pic etc. Once you make the changes, be sure to go down as far on the page as necessary to "submit" or "save" them (I forget if it's the same for each item).