How to Cancel an iTunes Preorder
You can cancel your iTunes pre-order from the Manage Pre-Orders screen of your iTunes Account. According to the iTunes Store Terms and Conditions, all purchases made in the Store are final. However, pre-orders can be cancelled because you are not charged for a pre-order before the item becomes available. Although you can cancel a pre-order through iTunes on your computer, the option to manage pre-orders from the iTunes app on an Apple device -- such as an iPad, iPhone or iPod Touch -- is not available.
Press the "Alt" key to reveal the menu bar, and then open the "Store" menu.
Select "View Account," and then enter your Apple ID password.
Click "Manage Pre-Orders" in the Settings section. This will display a list of items that you have pre-ordered on iTunes.
Locate the pre-order you want to cancel within the list. Click the "Cancel" button next to it, and then confirm the cancellation when prompted.