Once an order has been placed it cannot be canceled or modified. 

However, if you are not 100% satisfied with your purchase, you can return it for a full refund (you must pay for shipping costs) within 30 days as long as the product is unused and in its original packaging.

If you ordered the item on Amazon, you can request a cancelation if the order has not shipped. Log in to your Amazon account, and request the cancelation directly through Amazon.