How do i delete a clients credit card and add a new one?

Hi there rph2,

 It's vital that all your transactions be entered properly for your books to be well balanced. QuickBooks Payments is a great tool able to help you process payments for the services you provide your customers. I can point you in the right direction for assistance with updating this customer's payment information.

For help in changing the credit card number for your customer so you can process it on their new card, I recommend reaching out to the QuickBooks Online support team outside of the Community. They'll be able to best assist in updating this information so that you can make sure the payment is done on the right card. You can reach them using these steps:

Schedule a Callback or start a Chat: click (?)Help in the upper right > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat.
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If you have any other questions, feel free to reach out here.