A refund may not be possible since the terms of sale for the iTunes Store state that all sales are final. You can contact the iTunes Store, explain the reason for your request, and ask, though:
It's possible they'll make an exception for you. An exception is more likely if the app is defective in some way or doesn't do what the developer advertised and the developer has been unable or unwilling to help you. If you just don't like the app, a refund is not likely.
Forum Tip: Since you're new here, you've probably not discovered the Search feature available on every Communities page, but next time, it might save you time (and everyone else from having to answer the same question multiple times) if you search a couple of ways for a topic, both in the relevant forums and in the Apple Knowledge Base, before you post a question.