how to change payment method for icloud storage?

This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on an Apple mobile device, a Mac, or a PC; click here --> https://support.apple.com/HT201266

- If you are updating an old card and have ongoing subscriptions you may need to first add the new card and make it the primary payment method before deleting the old card.

'If you can't remove your last payment method or use no payment method with your Apple ID' click here --> https://support.apple.com/HT203905

If you still have problems Click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232

Additional resources:

'Payment methods that you can use with your Apple ID' --> https://support.apple.com/HT202631

'If your payment method is declined in the App Store or iTunes Store' click here --> https://support.apple.com/HT203005

muguy's URL wasn't posted as an active link. Here is it active: https://support.apple.com/billing

Realize the information I provided is how you change the payment method. The link muguy provided simply takes you to general support for subscriptions and billing.

Apple tucks iCloud subscription changes in its own area, not with other subscriptions, but it does not include altering the payment method because it is all done in the same place as others.

You cannot select a payment method for iCloud alone. Downgrade or cancel your iCloud storage plan - Apple Support

In your payment methods list Apple will automatically try using your Apple ID balance first. It will then work its way down the list of cards or whatever you have until it finds one that works. If none work it will keep on trying. If a card isn't working and you want to remove it, read the link I provided. To re-prioritize I suspect you just tap on one and drag it (I have never had to do this so I don't know).

Visit support.apple.com/billing