I see no option to change my payment method within an exisiting app/software subcription in iTunes.

I recently purchased MS Word/Office 365 Personal through the Itunes store. I also have an Evernote subscription on iTunes. I now want to change the payment method to a different Visa card that I have on file on the Itunes Store. Is this possible, or do I need to delete the subscription and repurchase with the desired payment method?

Thank you for any insights on a solution.

Sincerely,

Paul