Yes - as Rokrdude says you can do this by pressing on the 'button' at the top of the web page that says 'User CP' (User Control Panel) and a panel will open up on the left hand side of the screen where there's a whole range of controls that will enable you to update your personal profile and add a pre-set picture (avatar) or upload one. You can only do this from a regular web browser not the iPad Forum app. If you want to upload your own picture, too, rather than using a pre-set avatar you'll need to do it from a PC as it's difficult to upload pictures from an iPad.