The information you can revise depends upon the time you have left before your listing ends and whether your item has had bids or purchases.
If your item has received no bids or purchases and does not end within 12 hours, you can revise anything in your listing except the selling format (for example, you can't change your auction-style listing to a fixed price listing).
If your item has received a bid, a purchase, or ends within 12 hours, you can only:
Add to the item description or add a second category
(Exception: If your listing has a bid and ends within 12 hours, you can't add to your description or add a second category)
Add optional seller features to increase your item's visibility.