To replace or change the images within the template of an active listings, you can revise the listing via the following steps:
1) Locate your listing in your Saved Listings folder, make any necessary changes, and save.
2) Check the box next to your updated listing in your Saved Listings folder and click the “Get html” button.
3) Select All and copy the html in the popup window.
4) Locate the item on eBay and click the "Revise Item" button.
5) Click "Edit Description" then click the "Enter your own html" tab above the description editor.
6) Delete the html that is already there and then paste the copied html in its place and save you changes.