Q: how to do updates on iPhone without using credit card

Howdy sharitad,

Thanks for using the Apple Support Communities.

If you're being prompted to enter payment information when downloading an app or updating one, then it indicates that your current payment information is either empty or it is invalid.  A valid payment method is required with an Apple ID if you have a payment type already added to your account.  You can however change your payment type to None by following the directions in the article below.

Change or remove your Apple ID payment information

Take care.