Step 1: Tap on the Play Store icon on your home screen
Step 2: Tap on the "Menu" in the Play Store application
Step 3: Tap on "Account"
Step 4: Tap on "Payment Methods"
Step 5: Add your payment method
The instructions above are for users that have upgraded through the Google Play Store.
If you have purchased your subscritpion directly with SurfEasy you are able to update your billing information from accounts.surfeasy.com/profile