You can revise certain details in your active listing depending on the listing format you're using, the time left before your listing ends, and whether you've received any bids or purchases. There's no charge to revise a listing, unless you add a special feature or raise your asking price.
For most listings, you can change the title, add or change photos, and add optional listing upgrades at any time. For fixed price (Buy It Now) listings and auction style listings with more than 12 hours left that have no bids, you can also lower the price.
In most cases, you can't change the listing duration or format. For example, you can't change a fixed price listing to an auction-style listing.
To revise a listing, go to My eBay > Active Selling. Find the listing you'd like to revise, then from the More actions drop-down menu, select Revise. Make your changes to the listing, then select Revise it.