My Nexus 7 (2013) was just updated to Android 4.4.3 two weeks ago. It is Android 4.4.4 now.
Followed the prompt, the system is safe to upgrade. Be sure, the batter is full charged or with usb power connected.
System update downloaded is done. Time to upgrade.
It said 2.4MB data was downloaded. Touch Restart & install
After shutdown and restart, and optimize the installed apps. Go to the settings, about to check the system information.