You need to go to the image management page to do this. Here is the link
http://www.auctiva.com/hostedimages/imagemanagement.aspxYou can only edit one photo at a time and Auctivas editing functions really stink.(Sorry Jeff, but not much functionality there) I personally use Irfanview which is a free download.
The only thing you can do with Auctiva is resize your pics and crop them.
BTW are you talking about a active listing here?If so a link would possibly help to identify the problem.
Most of the time if it is active it is easier to fix through eBay using the revise listing feature.