You can edit your payment method in your account settings.

1. Open the Play Store.
2. Tap menu > Account.
3. Choose Payment methods > More payment settings.
4. Enter your Google Payments account if asked to do so.
5. Tap menu in the browser > Payment methods.
6. Tap Edit under the selected payment method.
7. Apply the changes and tap Save.

For the Amazon Appstore:
1. Open Manage Your Content and Devices.
2. Select Settings > Edit Payment Method.
3. Enter your changes and tap Continue.