Hi William, I am currently in the process of updating my MC40s from JB to KK. I am using a ZIP called M40N0KXXVRUxx20701.
It's a bit tricky to get it going the first time but you have to do this to get it going:
Hold the power button down until the window pops up where it says: power off, reset, airplane mode, etc
Now, with your left hand, hold down and keep holding the scan button thats on the left hand side of the device. The button with the white line going through it.
While you have that held, hit the "Reset" option. Keep holding the scanner button until you make it into recovery mode.
From there, navigate to where you put M40N0KXXVRUxx20701.zip and install it. So you install this first. If you want to do a clean/wipe of the device, you need this file M40N0KXXXRF0000001.zip. You would need to boot the scanner up after you install the update and then reboot back into recovery mode doing the same process.
This time, when you hit the scanner button, you will get a laser emitted and it will stay on until you install the wipe and then reboot the device again. But there ya have it, now you're on KK.