I don't think you can. Before you bid, you are warned that this is legally binding. All you can do is hope someone out bids you.

I don't think you can unless it was a typo (like you meant to type 11.55 but you typed 1155). Sometimes if you write the seller they will let you out of the bid.

From ebay itself: http://pages.ebay.com/help/buy/bid-retract.html When you are the winning bidder, you are obligated to pay the high-bid price for the item. As a rule, retracting bids is not allowed on eBay. Remember that all bids on eBay are binding, except: * Sales of real estate or businesses (see the Non-Binding Bid Policy) * Sales of items that are prohibited by law or by eBay's User Agreement Exceptional Circumstances Only There are, however, a few exceptional circumstances (described in the User Agreement) 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. Please review the retraction guidelines if you need to retract your bid. * 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. Timing Matters There are special rules about retracting bids, depending on when you originally placed the bid. If you place a bid before the last 12-hours of the listing: You may retract that bid before the last 12-hours, if your situation meets the above description of exceptional circumstances. You will not be allowed to retract that bid during the last 12-hours of the listing. When you retract a bid before the last 12 hours of a listing: You will eliminate all bids you have placed on that item. If you are correcting a bidding error, you will have to bid again. If you place a bid during the last 12-hours of the listing: You may retract the bid only within one hour after placing the bid (and if your situation meets eBay's exceptional circumstances description). When you retract a bid within the last 12 hours of the listing: You will eliminate only the most recent bid you placed. Bids you placed prior to the last 12 hours will not be retracted. If you are not allowed to retract your bid during the last 12-hours of the listing, you may contact the seller to request that your bid be canceled. The seller will have the discretion whether to cancel your bid. Accountability Your total number of bid retractions in the past twelve months is displayed in your Feedback Profile. eBay will thoroughly investigate bid retractions. Abuse of this feature may result in the suspension of your account. Bids retracted within the last 24 hours of a listing can be viewed as bid shielding, which is a serious violation of our policy. How To Retract a Bid To retract a bid, use the Bid Retraction form.

You can't retract a bid. Hopefully, someone will out bid you.