How to update my bios asus maximus 2 formula

It should be in the motherboard's manual.
Anyway,there are 2 ways of updating the BIOS
1)There is a software in ASUS website(it's called ASUS update).Download it and then download the latest BIOS,then open the app and follow the instructions

2)Another way is to download the latest BIOS and copy it to a flash drive,then reboot and go to the BIOS.There should be an option called EZ flash(or something like that),there you locate the BIOS file which you copied to the flash drive and it will update the BIOS.