How to change my regular SIM card to Nano-SIM?

I'm currently using 3G prepaid SIM card, I would like to know how do I change my regular SIM to Nano-SIM for the iPhone 5?

Not possible. The chip layout and contact points are slightly different for nano-sim.

You may have heard in the past that it is possible to convert regular sim to micro-sim. That is because for micro-sim, the chip design and size is still the same. The only difference is the size of the outer plastic housing. Hence, it is just a matter of trimming the plastic housing to smaller size.

But for nano-sim, we're basically out of luck. The safest bet is to ask for replacement via telco. My guess is that even if there's a way, it won't be elegant.