I need to up date my credit card details

Changing your payment information using an iOS device

1. Tap Settings on the Home screen.
2. Tap iTunes & App Stores.
3. Tap your Apple ID. (If you aren't signed in, enter your Apple ID and password and tap Sign In.)
4. Tap View Apple ID.
5. Enter your Apple ID password.
6. In the Edit section, tap Payment Information.
7. Update the information that you want to change.
8. Tap the Done button when you're finished.

Thanks

MY card was changed I need to up date it

See : Change or remove your Apple ID payment information - Apple Support