That is not the latest version of JB, 4.2.2 is. There may be a future update for you. Why do you want to root? You will not be able to use the OTA update process if you root.
I also want to know this b/c I want freeze and remove bloatware. I like the JB upgrade and don't even care to flash a ROM but my battery life has gone down probably 30% since the update and Adroid OS, which was normally <10% of daily battery, is now always at least 60%. Before, I could make it a full day at work and not be below 90% and I'm at 90% now after 1 hour 30 minutes off charger. Granted I'll be at 70% when I leave at 5:30 but still.....
I have seen a video and a different forum that has this info but I want to see if anyone here has done it yet. I just want my battery life back haha. It was my favorite thing about this phone.... well not really but I really enjoyed never being below 50% after the day was over.