Assuming they are actually uploading.........You probably need to log out of both the main site & the forums, clear your browser cache (ctrl+F5) then log back in to both the main site and the forums.......and you need to give them time to propogate across all the servers.
This was true of the old system (and attempting to update via your personal wc site/main wc site), however it's not true of the new system (impulsedriven.net, joeuser.com, forums). On the WC Personal Sites, updating your personal images is pretty much broken at the moment. Although, some people have had to use CTL+F5 after uploading on the forums. Seems that there are some agressive browser cache's out there
I would reccommend updating your images from the forums (http://forums.wincustomize.com or forums.whateversiteyourvisitingfrom.com)
//Moved post to Wincustoize Site Issues