This question already has an answer here:
I mistakenly installed 5.0 Lollipop on my NVIDIA SHIELD tablet, and I hate it. Is there a way to revert back to KitKat? I've tried finding a way, but no luck so far.
This was the original post: Downgrade nVidia Shield to Android 4.4 KitKat
StackExchange doesn't let me comment or reply to this question because I don't have enough reputation... so I am forced to create a duplicate.