No, you can't, sorry. You see, a bid is binding. This means that you cannot cancel or reverse a bid that you have placed. Only auctions with the right of withdrawal can do that (we'll tell you more about that below).
Does someone else place a higher bid? Even then the seller or client can hold you to your bid until the day on which the lot is picked up.
We have clearly set out our rules for you in our general auction and sales conditions.
Exception with right of withdrawal
Sometimes you have the right to cancel your purchase after the auction closes. In that case please send us an e-mail.