Note: This does not upgrade the firmware version of the NVR, only the Unifi Video software.

Background

It can be troublesome to update the Unifi Video version on an Ubiquiti UVC-NVR (UVC-NVR-2T) beyond Unifi Video v3.9.12 using the built in webUI.

IMPORTANT:
Before proceeding it is highly recommended that you backup your data and recordings.

Use of this process is done entirely at your own risk.

Run the Script

Snappernet have made a script available to greatly simplify the process of upgrading your existing NVR appliance running Unifi Video or AirVision to the latest UniFi Video Software 3.10.x or above.
A clean install option (recommended) is also included.

You will need to enable SSH on the UVC-NVR and then login to the NVR via SSH.  
The default SSH credentials are root / ubnt but you should use the ubnt username along with your assigned password.

Run this command in the SSH terminal. Ensure that the entire block of text is included as one line.

Execute that command and follow the onscreen instructions.