Here are instructions from ninth_wave on another thread, about pics but works the same. Thanks Ninth.
"The method I prefer is to revise your saved listing in Auctiva, and then copy & paste the HTML from the revised listing into the description box of your active listing. No extra charge for this either. Here are the steps:
1) Locate your listing in your Saved Listings folder in Auctiva, open it, make any necessary changes (add the new photos), preview, and save.
2) On your Saved Listings page, click the <HTML> icon to the right of your listing.
3) Select all of the HTML in the popup window and copy it.
4) Locate the item on eBay and click the "Revise your item" link.
5) Click the "HTML" tab above the Description box.
6) Select all of the HTML that's there, paste the copied HTML in its place, and save your changes.
Keep in mind that you can only change your listing if there are no bids and more than 12 hours left on the auction."