If you still want to used the dated WiFi tether third party app, then you want to stay on MC2. It won't work on MK4. If you've already gone to MK4 there's a thread out there that has the files to flash in recovery to go back to MC2.
BEFORE UPDATING TO MK4 I'd suggest using triangle away. Reset the flash counter, and then flash the MK4 firmware. This will give you the latest stock (knox) bootloader, latest stock recovery, and latest system.