How to transfer my old number to my new sim?

I had a standard SIM card, but got a microsim for my iPhone 4S, so how do I transfer all my data off one sim to another one, so my micro sim will have my old number instead of the one already on the sim.

Added (1). I gotta be possible because I did it once before but I can't remember how, plus my sister transferred her number from a standard sim to a micro sim then to a nano sim.

That is not possible
you can request a micro sim for your number from the place you bought the same
you can't transfer a number from sim to sim
you can transfer data like contacts
but not the number

If its a different network you need to phone and get a pac code for the standard sim then fone the network for the microsim and theyll change it over for you. If its the same network you don't need the code just fone them up or go into the shop and theyll swap it over for you.