Lori, the picture, I believe you are talking about is called your Avatar. At the top of the page you see where it says Recent Topics, Search, Member listing, etc? Well it also says My profile. Click on My Profile, Fill all of that good stuff in about yourself and at the bottom under Avatar Control Panel, you can click on browse and upload a picture from your collection or from somewhere else on your computer. Then hit submit. Remember, your picture cannot be any bigger than 130x130 pixels, if it is bigger, it won't download.
Hope this helps. :D