The listing info will not change in Auctiva, it is what is on ebay you need to be concerned with. As long as it shows the correct auction you are fine. You more than likely just double posted, The showcase and gallery should reconcile within 24 hrs, if not contact Auctiva throguh the help section and open a support ticket.
Now if you wish to change pics in your auctions once posted, you need to learn HTML. That is the only way you can get around the picture hosting fees to ebay. There are planty of free sites that offer HTML for beginners so you can get an idea of what to do.
Now if that was the only auction using those pictures, you can go to images and replace those without being charged, but then those originals will no longer be hosted here.
I hope this all made sense, you will get the hang of it in no time.