If you want to remove a card from your account you can do so directly from the Account section.

Scroll down until you find the Payment method section locate the card you want to remove and select Delete on the right of the card.

If you use your phone, rotate the device horizontally to display options

IMPORTANT: you will not be able to remove a card until there are still unpaid installments. You can remove the card after all installments have been paid in full.