You can redeem your promotional code directly on your iPhone. Make sure that your iPhone is able to connect to the internet before following these steps.
1) Launch the “App Store” application.
2) Select the “Featured” tab on the bottom option bar (see picture below).
3) Scroll to the bottom of the page and tap the redeem button.
4) Enter the promotional code you have been supplied with in the input field and tap the redeem button in the top right corner.
