Save the OS ?

[CarpCatcher]

I have a LG Optimus One (P500) and its running Andriod 2.2, the phone is unbranded and i would like to save the OS so when i upgrade to 2.3 i can always revert back if im unhappy with 2.3
I have googled this but it always ends up with info on how to save apps or settings but i want to save the OS itself.

Any helps apreciated.

 

[A.Nonymous]

You'd need to root and take a Nandroid backup first.