How would i get a new sim card?

Currently i have the iPhone 4S which has the micro-sim card, even though i'm still on contract i plan on buying the 5S off contract, the question is where and how would i get a new sim card, since the 5S runs with a Nano-SIM, also my carrier is AT&T. Would there be any fees?

You can go to the server company that you want and ask for a sim card, I guess.