In a Timed Auction, you will only be able to lower your bid amount to the next highest bid increment but not remove it completely if there are other existing bidders bidding on the same lot. This allows you to be outbid should an underbidder bid the next increment. You may however contact the auction house or Bidsquare directly to request that the bid be removed completely.
If you would like to place a new bid on the same item after retracting/canceling your bid - you may do so.