The underlying OEM firmware for this build is pre-rooted, so this is too.
The updater is signed, and so can be installed in the Update app, the stock recovery, or TWRP. It's designed for incremental updates, since user data is preserved. If you're installing for the first time, you should include a data wipe.
The safest bet is always to install the full Amlogic burn package with USB Burning Tool. With no reset switch, you can trigger USB detection by typing "reboot update" in a terminal window.
The local terminal app shows after being enabled in Settings->Developer Options. (This must be revealed by clicking Settings->About->Build 7 times.)
Flash ROMs at your own risk and always remember to back up your data first. The burn package includes a factory reset.