If you are having trouble processing app payments, it could be due to insufficient funds on your primary payment account, which can result in your account getting disabled.

This step by step guide with images covers how to change the Apple ID you're using with the iTunes and App Store on iPhone.

In that second screen, tap iTunes & App Store. Tap the Apple ID at the top if an account is already logged in. Tap Sign Out. Then tap to sign in and enter the shared-purchase Apple ID account.

If you went through iTunes to create your account, open the iTunes app and tap Settings > iTunes & App Store > Apple ID > View Apple ID to get to the iTunes subscriptions screen.