Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
Don't unplug it or turn it off when the unit is stating Updating...it's downloading software or firmware to it, and it needs to complete. If it gets unplugged or it crashes, it can damage your present operating software.
It's been updating now for several hours - how long do I leave it?
It should have taken no more than an hour and 15 minutes for a major firmware update.
Now the question is, was this update done wirelessly, or using a Lan cable or done with a USB stick?
You might as well unplug the TV's power cord for 20 minutes and see if the TV recovers from a bad download.