Very likely you cannot return it. In the U.S., if you buy from an Apple Store, I'm quite certain you get a 14 day return privilege.
You could purchase an iPhone 5S and sell your iPhone 5.
In the U.S, if you bought it from an Apple Store, you got 30 days and elsewhere only 14 days to return for full refund.
If you bought it somewhere else you have to ask for their return policy.