If coming from JellyBean and have not updated your recovery since, you will need to install the recovery provided below, otherwise this step is not required to install the KitKat update over an existing version of JellyBean / KitKat.
Recovery Update
The install requires removing the assert checks since there is an error that the device is a Thor but looking for a Roth (same thing, right?). Install this from the new recovery.
KitKat Update 72
KitKat Update 98
KitKat Update 99
Immediately after installing the update, install the SuperSU recovery package to restore root and you're all set.
http://download.chainfire.eu/supersu
XDA:DevDB Information
Nvidia Root-Friendly Updates [No Wipe], ROM for the Nvidia Shield
Contributors
twistedumbrella
ROM OS Version: 2.3.x Gingerbread
Version Information
Status: Testing
Created 2014-11-08
Last Updated 2014-11-08