[Q] How do i turn back to clean stock rom

Here I can't really find the correct answer for this (or i just don't understand it)
I want to remove EVERYYYYTHING in my phones and sd card
Include the apps and roms too
And return to factory stock

I don't want to backup anything at all
(except sync my contacts)

I already download my stock roms
But of course i still do nothing with it

I am using Ultimate N7000 XXLSZ JellyBean 4.1.2 v5.2 But it seem to eat more battery than i needed
Even turned off about 2 hours it drain 3 percents battery
And turn on = EXTREMELY fast drain (with screen on)