XDA is a developer site just like this one (droidforums), but larger and covers more phones. MtMichaelson is a developer for the LG Revo specifically. He is the man.
Download all of your drivers for the phone. turn on usb debugging and tether phone to computer in "internet connection" mode. First you have to flash clockworkmod onto your phone first, then download MtMichaelson's All-In-One root program and run the .bat file. You'll have the option to root, unroot, stock recovery etc. Chose the option that you would like to do. In your case you want to update to ZV8 and root, so i believe you will have to put ZV7 back to stock first which is an option in the program. untether phone, update to zv8, then apply root once more. I recommend flashing Mt's Broken Out Revo ROM. It's pretty much stock Gingerbread with no bloatware. Let me know if you run into any trouble.
This link is for Mt's All-in-One program:
***Easiest Method for Keeping Root Thru the ZV8 Update*** - xda-developers
This link is for Mt's Broken Out Revo rom:
[Rom][4-2-12][ZV8]Broken Out Revo 1.1 - xda-developers
This link is for the new Blitz kernel so you can undervolt and overclock your cpu. You will have to flash this in ClockWorkMod recovery. do this after you root and get his rom on your phone:
http://db.tt/wRYwpwNF