Looks like you already know how to edit your profile from the Control Panel.
Go back to your CONTROL PANEL ( you can simply click on your Private Messages link at the top right of this page to get there)(Or simply click on USER CP in the blue bar above). Then on the left side menu are many choices including EDIT PROFILE PICTURE which allows you to upload a picture from your computer. ( Choose File).Or you can add many pictures there by choosing PICTURES AND ALBUMS
Or you can add a picture to your name every time you make a post by choosing EDIT AVATAR ...(like the monkey pic on mine).