Click your subscription details link to get to "Edit Subscription" menu (If you can't find the link to click, hover your mouse near to the Edit Subscription words until a hand-click icon is shown):
Select "Update Payment Method" and click "Next".
Update your credit card details accordingly or input details of your PayPal account. Then click "Update Payment Method".
Here you will see all details of your order:
Switch to Account Details and Payment Methods to see what payment option you currently have on file:
If you need to add a new card or tie a PayPal account, you need to remove current payment method and add a new one: