IPhone 4 - iPhone 5 sim card change?

So my friend just purchased the iPhone 5 and doesn't like it. She wants to trade with me, and take my iPhone 4. The thing is, i would need a different sim card because the iPhone 5 has a new 'nano-sim' now and my old sim wouldn't fit. Is there a way i can turn my existing iPhone 4 sim card into an iPhone 5 compatible? Because i'm unsure if AT&T will allow me to 'trade' phones without upgrading my contract. Do you know where i could change it or if AT&T will not allow me to change? Any help, answers, or suggestions would be greatly appreciated.

Yes just shave the back down to fit, be careful

You can cut it down to size.
Here's a good site showing you how to do it
http://www.redmondpie.com/how-to-convert-micro-sim-to-nano-sim-for-iphone-5/

Now if you cut it you won't be able to get LTE. In order to get LTE you would need to call AT&T and tell then you have an iphone 5 and to activate it. I have no idea if there's a fee for this. You would have to ask AT&T. But they might make you get a new nano sim and tell you they can't activate LTE on your SIM card because its not compatable. Now if you don't mind having LTE (which is an extremely fast data connection) and are ok with 4G then cut the sim and swap with your friend. No need to call AT&T then. Your friend would need a nano sim adapter which can be bought on ebay for cheap. This adapter will make the iPhone 5's sim fit in your iPhone 4.