Updated for 7.0
Click on the Settings icon (the gear) located to the right of the search bar. This will take you to this page:
With the Accounting box, select Payment Types. This will take you to this page:
To add credit card type, click the + Add button in the bottom right-hand corner.
Type in the name of the new credit card type where it says Name.
To the right of the name, type in the fee of the credit card.
To make a credit card type inactive, click the button to the right of the fee that says ON.
When done, click the Update button in the bottom right-hand corner to save changes.