Hello 'madawaska',
You are not supposed to withdraw a bid, not if it's your own you have placed. But if you
insist, -- there are few reasons considered 'valid' whereby you can retract. The following
link tells you all about this, and there is a Bid Retraction Form you can use:
http://pages.ebay.ca/help/buy/bid-retract.html
If, however, you are the seller and wish to remove the bid of someone else, that too
is not recommended, but certainly more forgivable, odd as that sounds. There's this
http://pages.ebay.ca/help/sell/manage_bidders_ov.html#canceling
