I think if you are talking about your username you need to get the assistance of Jon or a moderator.
As for a picture...are you talking about a little avatar-like thing under your username? To do that, do this:
1) In the top right corner of the screen, you'll see a My Cpanel. Click that.
2) Down the left hand side of the screen that pops up there will be a menu. One of the options will be Edit Avatar. Click that.
3) Click the Use Custom Avatar radio button, then put in the link of the picture you want or directory from your computer where the picture is located.
4) Click save changes.
5) Voila!