You have 14 calendar days to return an item from the date you received it. for any reason. Only items that have been purchased directly from Apple, either online or at an Apple Retail Store, can be returned to Apple. Apple products purchased through other retailers must be returned in accordance with their respective returns and refunds policy. For more info, see:
Returns & Refunds - Shopping Help - Apple
If you purchased your item from Apple in the U.S., you can take it to any U.S. Apple Store for an exchange. Item exchanges are, of course, subject to in-store product availability. It's a good idea to check if a product is in stock by visiting apple.com and then seeing if it's available for pickup at a store nearby.