If you had already bought the Samsung, returning it might be a bit hard. Even if they allow you to return it, whether you can exchange it for another phone depends on the store's exchange policy, and you will probably be required to part with some cash. Check your carrier's return/exchange policy for clarification.
most likely not without spending money for the price difference if there is one. you already bought that phone so they wont let you trade it for a new one. then they lose money cause that phone you have is now used and they can't sell it as new.