Can I upgrade from 16gb to 64gb and change colour for an already purchased phone (unopened)?

[iMore Question]

Basically I got an iPhone 6s for Christmas which I'm SO happy about, it's my first iPhone, I still don't have a contract or anything yet though. However I got it in the color Gold, which I first thought I wanted, now I'm thinking it's a bit too bling and I would prefer Rose Gold. Also I got the 16gb version, I would prefer 64gb and I'm happy to upgrade it for the cost myself. The case is completely unopened as of yet. Is there any way to exchange this? I'd rather not ask my parents for the receipt as I don't want to hurt their feelings by basically saying "this isn't exactly what I wanted" when they've spent loads of money on my Christmas present. So yeah, that's my question basically. What do I do?

 

[Highrisedrifter]

Yes if they got it from the Apple Store, I believe you can take it back and they can verify that it was bought from Apple by checking the box's serial against their sales recepits. Don't open the box though (even though Apple say you can as long as you return it undamaged and with all accessories). You can pay the difference.