To edit a credit card, sign in and go to My Account. In the left hand menu, you'll see Edit Credit Card--click on that and you will be taken to your list of credit cards vaulted on our credit card processor's PCI compliant servers. You'll see a link next to your card to Edit or Delete your card. Click on Edit to edit the number or expiration date, etc.
To Delete your card, do the same as above but click on Delete instead of Edit. Please note, you cannot delete a card that is associated to a bid on an open item or a card that is related to an unpaid item. You'll need to either add a new card and edit the bidding options on that item to use the new card (once a new card is associated to the bid on the open item you can delete the old card) or just wait for the item to end and delete the card once the item has closed. If you have an unpaid item associated to the card, you will need to add a new card and pay for the item before you can delete the old card.