Apple ID is a personal account to access Apple services like the App Store, iCloud, iTunes Store, iMessage, FaceTime, and more. Each Apple ID can only assign a credit card for using with iTunes, the App Store, iBooks, and other purchases you make via apps on your iDevices. You can also update your billing info on iPhone and select a different credit card for iTunes and your Apple ID. When you change your Apple credit card or billing address, your information will also be updated everywhere you use your Apple ID.
Here is how to change your Apple ID credit card for iTunes on iPhone/ iPad
Step 1: Open the Settings app from your Home screen
Step 2: Select iTunes & App Stores
Step 3: Tap on Your Apple ID at the top
Step 4: When the pop-up displays, tap on View Apple ID.
Step 5: You will be prompted to enter your Apple ID password.
Step 6: Then, tap on Payment Information.
Here, you complete all information of the new credit card you want to use for iTunes.
Once all the information including the billing address with your credit card is complete, tap on Done at the top right corner. Then tap on Done again to quit Apple ID Account Settings.
Now you have a new credit card for use with iTunes, and any other apps on your iPhone/iPad
Besides, you can also update your iTunes credit card on your computer by doing this on the website of Apple. This credit card is also used for purchases on your iPhone, iPad, and in iTunes. Any time you are asked to enter your Apple ID password to complete the purchase, this credit card will be the one being charged, therefore, importantly you need to keep it up to date. To update the iTunes credit card on your computer, just follow the simple steps.
Step 1: Go to AppleID.Apple.com
Step 2: Here, log in your Apple ID account as well as password.
Step 3: You will be taken to a page with all of your Apple ID account info.
Step 4: Scroll down to find Payment & Shipping. Then, click on Edit Payment Information
Step 5: The page will be expanded and display all the billing info. You just enter the payment info for the new credit card you want to use for iTunes, including the billing address associated with the credit card.
Step 6: when you finish, click on Save.
Now, every time you pay for something from the iTunes store, App store, or in case you want to make an in-app purchase, the new credit card will be charged.