Hello Ken,
The picture in the template should just be written out as HTML code in your description. If you find that you can manually change the URL to point to your new image.
If your images are hosted by Auctiva, Auctiva also offers a "Replace Image" button on the Manage Images page that will allow you to upload a new image to replace the old one in all your current listings.
Let me know if I answered your question,
Auctiva David