When you get to the screen that says can't find device, that is when you should turn off the unit and turn it back while holding the side button until the USB symbol appears. I had the same problem you described and this worked.

Plug your USB cable directly in to your computer, not a hub.

It upgrades fast if you download the file first, then do a manual upgrade. At the screen that lists the OS versions, click change and point it to the file you downloaded. Takes about a minute or so.

Good Luck