Changing Your Bid
The way that you change your bid depends on whether you’d like to raise it or lower it.
You can raise your maximum bid at any time before the end of a listing.
To raise your maximum bid:
Click My eBay at the top of any eBay page. You may be asked to log in.
From the left column of My eBay, click the “Bidding” link.
In the Action column next to the item you’re interested in, click the “Increase Max Bid” link.
Follow the instructions on the next page.
When you are the current winning bidder in a reserve auction listing and the reserve has not been met, your bid may be raised if you place another bid that meets the reserve amount. This allows the listing to end successfully.
In order to lower a bid you will need to retract your original bid first and then place your lower bid.
There are only a few exceptional circumstances under which you may retract a bid. These are if:
You made a typographical error and accidentally entered the wrong bid amount. (Changing your mind is not considered a typographical error.) For instance, you bid $99.50 instead of $9.95. If this occurs, re-enter the correct bid amount immediately after you retract your bid. If you do not place another bid, the retraction will be in violation of eBay's policy and could result in your suspension.
The description of an item you have bid on has changed significantly.
You can't reach the seller. This means that you tried calling the seller but the seller's phone number doesn't work, or you have tried emailing a message to the seller and it comes back undeliverable.
Please review the retraction guidelines if you need to retract your bid.