Is there any way I can bring iPhone 5s ordered online into store, and change colors?

I ordered my iPhone 5s in silver last Friday, and was planning on canceling the order and reactivating on a new space grey model. However, my order has shipped faster than expected, so I can no longer just cancel the order. Do any of you guys know whether or not I can just go into a store, and switch the phones as long as I don't open the package? this was through AT&T by the way.