If you signed up on your iPhone:
- Go to Settings > Apple ID, iCloud, iTunes & App Store > iTunes & App Store.
- Tap your Apple ID at the top of the screen.
- Tap View Apple ID. You might need to authenticate your Apple ID.
- Tap Manage Payments.
- Then make your changes.
If you signed up on your Android device:
- Open the Google Play Store.
- Tap Menu > Account > Payment Methods.
- Find the subscription you want to update.
- Tap Update.
- Then make your changes.