Hold Select on boot and make sure that the version string option in Settings is ticked. Don't update unless you see emu.
To boot into sysNAND you can do what you did or hold the button that makes you boot into sysNAND (you would have chosen this when you set up menuhax).
And yes overwrite anything that you have to, but make a backup of your SD contents before you start in case you change your mind partway through, then it's easier to go back to how you had things.
Thanks man your being very helpful. I do think that I'm gunna go for it and instal a9lh now that i see i dont have to downgrade to 2.1.
I only have one last question. I noticed while reading the tutorial that a9lh does not use emuNAND. So if i make a backup cant i just format my SD card to make things a little easier, as my SD card is still full of crap I dont know about. And emuNAND takes up the whole card.