Kevin,
go to:
http://offer.ebay.com/ws/eBayISAPI.dll?RetractBidShow
then enter your user name and password and it will walk you through it from there.
Be sure before you do this that you write down the item # as you will need that. Also, do this ASAP because if the item ends within 12 hours of when you try, then Ebay will not allow it.
peace, mike