Visit the online Apple Store, go to "Gift Cards," and then "iTunes Gift Cards," to select the denomination of your iTunes gift card. Once you've made your selection, click on the "Add to Cart" option.
Confirm your order is correct. Click on the "Check Out Now" option.
Sign in to your Apple account. If you are new to the online Apple Store, enter your email address to create an account.
Enter your shipping and billing information. Once you've verified the information is correct, select the "Place my order" option. Your credit card will be charged at this time.
In the iTunes music store, click on the "redeem" link to redeem your new card when you get it. Once you've entered the new code into your iTunes account, you'll be ready to start shopping again.