Changing your payment information depends on the type of phone you use:
If you use WithU Daily on an 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.
Make your changes.
If you use WithU Daily on your Android device:
Open the Google Play Store.
Tap Menu > Account > Payment Methods.
Find the subscription you want to update.
Tap Update.
Make your changes.