If you mean as a buyer, you have to wait for the listing to end (which can be years for a fixed-price listing, especially a multiple-item one, so keep that in mind when you are deciding whether to make an offer vs. using the BIN button on that or another listing). Once it ends the entry goes down to Didn't Win section of the Bids/Offers page from which it can be Deleted by checking the check box for that listing and hitting the Delete button at the top (next to the checkbox to check all the listings).
