It's not changing the customer's credit card number

Q: I noticed that when customer gave a different credit card the program did not replace the old number under customer detail.  Why not?

A: If you're talking about the Guarantee info in Customer Details, then that's correct, it won't automatically change that if they use a different card for charges later, or if you change guarantee info in Reservation Details, since that's a separate record.  The Guarantee info in Customer Details is considered historical information, and won't normally be used for future payments.  

In fact, it's recommended that you set the Credit Card Security Settings so that the Guarantee Info credit card is removed once they check in (see Maintenance / Credit Card / Security Setup).