How to update asus p8 z77 v le plus bios

You can use the EZFlash in BIOS.
Set BIOS to default before flashing, so yes, all settings will be lost.
You can use the ASUS O.C. Profile, but check the Conclusion here:
http://www.pugetsystems.com/labs/articles/How-it-works-O-C-Profiles-90/