If you are in the need to change your payment details aand you have chosen 2Checkout as the payment gateway, you can do it by visiting 

https://www.2checkout.com/va/sales/customer/change_billing_method

You may have to select a specific sale or an order to complete this process and you can do so either by 

1. Search by Credit Card 
2. Search by Zip Code


After this, you will be taken to the page where you can update the payment information.