Click the dropdown arrow by your name and choose the Account option.
If you have purchased something before, you will have a credit card on file. You can view and edit that by clicking the Credit Card menu option. If you have never purchased anything, you will not see the credit card option yet as one is not currently on file.
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:
