how do I change my credit card info for storage

Hello grandma--4,

iCloud storage would come from your Apple ID balance first, then the card on file for your Apple ID.

In order to update or add a card, use one of the following, depending on your situation:

• If you need to change or update your Apple ID payment method - Apple Support
• Add a payment method to your Apple ID - Apple Support

Keep in mind: Payment methods that you can use with your Apple ID - Apple Support

Hoping this helps out.

Take care!