Launch iTunes on your Mac, then click your name in the top of the application. You should select the Account Info option.
Enter your password, and select the See All item from the Purchase History section.
Click the arrow next to the purchase line that you would like a refund for.
Click the Report a Problem button/link, and you will be routed to Apple's website. Follow the steps shown after signing in, and request a refund by explaining why you would like to return the product. If the refund is approved by Apple, you should see the funds returned to you in 5-7 business days.