How do I update my credit card information in Apple?

Cards in Apple Wallet app are maintained and updated automatically by the issuing bank when needed.

Cards on file with Apple in your Apple Account can be updated by the user. Please follow this path,

iPhone > Settings > Apple Account (your name near top of screen) > Payment & Shipping > tap card to update > Edit (blue link upper right corner) > update expiration date and security code (for security purposes the number never displays) > do not check security code for correct number > taping on dots erases code and you must start again