1)If you have no problem with your current system, DO NOT UPDATE YOUR BIOS.
2)If you feel that you have a problem and have done your best to solve it and the only thing remaining to be tried is the bios then:
1)Read whatever is written on the bios site, insturctions, drivers required etc.
2)Download the bios and the utility.
3)Make a back up of the previous bios.
4)Update the bios through the utility and saved file on the computer, not through the internet.
5)If something goes wrong while updating you can loose your mobo and may need to buy a new one.
6)Keep in mind that people are having overclocking problsm with newer bioses of asus a8n e, do google before you decide on a bios, I would say don't take 1013 as it gives oc problems, read it.
Unless you are having problems, do not update the bios. Befroe you can even think od updating the bios, make sure that you have tried things like formatting, newer nforce drivers, graphic drivers etc before you can blame the bios responsible for your problems.
It is something which is serious and not a joke. Asus has made it very easy to implement but its consequences always need not to so forward coming.