Can i exchange my iPhone 4s for the iPhone 5 if i pay the difference on it?

I had told my mom the iPhone 5 but she got me the 4s instead my mobile network is sprint and I've only had the phone for a week

You might be able to return it if you have the receipt. But call like best buy or wherever you bought it and ask them. It really depends on how long ago you bought it and how much you used the phone.