You don't root to upgrade. (And stop with the "old guy" stuff - I remember the day FDR died and I don't have to look at the computer too much to flash a phone. Old means pain, not inability to learn.) If and when Google releases an update, you'll get it (it's supposed to be upgradable to Lollipop, which I wouldn't let near my phone, or KitKat, which I'm running even though there's a Lollipop update available if I wanted it - which I do like I want another arthritic joint). Otherwise, head over to
Nexus 7 Android Development - XDA Forums and start reading the various ROM threads to see if there's one you like. (Some are faster, some are better on battery, etc.) If all you want is a new look, install a different launcher, some new icons and different wallpaper.