Sometimes a recurring customer's credit card on file will be updated or reissued, or the customer may want to change the card. If the subscription is set to recurring, there'll be an update link option on the customer's account page in MemberPress. Clicking the update link will allow the user to enter their new card details.
If the customer's recurring subscription is through PayPal Express Checkout or Standard, they'll need to update their card information in their PayPal account instead.