If you created the original listing using auctiva then it will be in your saved listings. You can edit your saved listing and select a template for it and then just save it.
Then go back to saved listings and check the box next to the new saved listing and click the Get HTML button at the top right. When the code box pops up click select all and then right click anywhere on the code and select copy.
Then go to your active listings and find your active listing you want to change and check the box next to it. Then click the revise button. Ebays editor will load up.
Once the editor has loaded switch to view HTML mode. Highlight the entire code in ebays editor and then hit your delete key on your keyboard. Then right click anywhere in the editor window and paste the code you copied from auctiva. Then scroll down and click the save button. when you switch the editor back to normal view..you should see your new listing with your selected template. then just go through ebays submit changes routine. You may lose your scrolling store window if you do this. Whenever I do this the store window does not show up anymore.
If your not sure about doing this, do not delete the code in ebays editor or your present listing will be gone.
If this is an imported listing from ebay...im not sure how that works as I have never edited an imported listing. If it is an imported listing please reply back here and maybe someone can help you with that.