You need to get a free gift code through the apple store app. Open the app and hit the Stores tab. The link should be in there.
You need to download the Apple store app first. Then open the app and click on the banner with Temple Run: Oz. Your Itunes (on your IOS device) will then popup with the promo code and you click redeem. Done
Despite being a movie tie-in, this is the best and most fully developed of the Temple Run games IMO. Don't let the Oz theme deter you from grabbing this one.