After you update your payment method, i Tunes Store automatically attempts any outstanding orders with your updated billing information.To see which order you need to pay for, you can view your purchase history on a Mac or PC.Here’s how to change your i Tunes credit card on your i Phone and on your computer.The process is the same if you want to know how to add a debit card to i Tunes in place of your credit card.* Note that It's actually possible to create an Apple ID without a credit card.
You will then see a form for entering your payment information, add your new card details on the right and click save.
One way is to go to click "Store" in the top menu and then click "Account" and "View Account" as in the below screenshot.
Under "Account settings" there is the choice to "Change your default shipping or billing info", click that link and then enter your Apple ID e-mail and password to login.
Do you have an i Tunes gift card that you want to use?
This article will show you how to redeem that gift card on your i Phone.
Changing your email address is trickier because it is your Apple ID.