You have to be logged in copy and paste the item number and go to this link: http://offer.ebay.com:80/ws/eBayISAPI.dll?EndingMyAuction
It will probably ask you to log in again, then you will see 4 categories to end your auction.
it's not a stupid question! It's hard to remember where everything is on eBay.
I always just click their "Help" tab at the top of the eBay pages and type in a few words to search, it always brings up whatever I'm looking for.