After signing in to your VetFolio account, clck the dropdown arrow by your name and choose the Account option.

If you have a purchase history: You will see a Credit Card menu option on the left side of the Account page to view and edit your card on file.
If you have never purchased anything: The Credit Card menu option will not appear until a card is added or a purchase is made.
What it looks like when you have a credit card on file:

What it looks like when you do not have a credit card on file:
