If no one has bid on your auction, you are able to edit or delete it through the selling section of the members' area. However, once someone bids on your auction, you are not able to edit or remove it except to add to the description. Make sure you are positive you want to sell your item before you put it up for auction; auctions are binding once they've gotten bids. If it's an emergency situation, you could contact the bidders and explain the situation, asking them to retract their bids. Understand that the buyers are not obligated to do so, however.