Once you list your item, you're not stuck with the same listing forever. If no one has bid on the item, you can revise the title or description, add or change an image, or change the category in which the item is listed. Look at the "Update item" section or your listing to revise it.

At any time during the auction, even if your item received bids, you can add text and pictures to your item description. You can also change the category in which your item is listed.