See also: How to install Windows 7 Before you start, heed this warning: if something goes wrong during the BIOS update, your computer could be rendered useless.
It's good to have a spare copy of all important files from your PC before you start.
For this reason, it's worth checking whether you really need to update your BIOS.
Read the release notes of the latest version (and each version back to the one currently installed) to see whether it will add the features you need or fix a problem you're having.
I would say, just go for it - some modern machines offer the ability to back up the BIOS and recover in the event of an error.
If however you don't have this option, make sure you have access to another machine so that you can download a recovery image or emergency image (different names across different manufacturers) so you can do a recovery if needed. Changing it back after flashing made Windows boot normally.
If not, there may be little point in taking the risk by updating.