The "problem" stems from the one bid you have. eBay does not allow certain editing if there's a bid already in place.
If your item has already received a bid/purchase, you can only:
Add to the item description or add a second category (exception: if your listing already has a bid/purchase AND ends within 12 hours, you can't add to your description or add a second category).
You can also add optional seller features to increase your item's visibility.