Open the App Store. From the menu bar click Store > Sign In
Then back to the menu bar click Store > View My Account
Click Edit for payment type then select None.
Be aware. The "None" option is available in the U.S., but not all countries.
When you purchase an app, the total amount of the purchase is deducted from the balance of a redeemed card first, the difference is charged to your debit or credit card account.
If you select None, the amount is automatically deducted from the balance of the redeemed card.
You can check the balance available anytime > Account Home - Apple Store
Message was edited by: Carolyn Samit
Actually the None option is available world wide*. However, not everyone has the None option available to them for reasons only known to Apple.
You don't have to remove your bank card as the iTunes/Mac App Stores (MAS) are set to use a credit on the account until it is exhausted before using any bank card stored on the account. When you get down to the last few dollars and cents on your credit balance the system will automatically use up the credit and then charge any remainder to your bank card.
iTunes Store: How iTunes Store purchases are billed -
*If someone follows Apple's instructions for creating a new Apple ID and iTunes/MAS account, they will always get the None option, regardless of the country in which they reside.
Creating a new Apple ID for an iTunes Store, App Store, iBookstore, and Mac App Store account without a credit card -