Before flashing any new firmware, take a note of your current Z-offset settings. See this related article before proceeding.
If your extruder has a RED band near the main connector it is a 24V extruder and you will need the Me2_HV firmware, otherwise use the LV firmware.
Me2_LV (12V Extruder) Download
Me2_HV (24V Extruder) Download
Connect to your printer using MatterControl as normal and then navigate to the bottom of the "Control" tab. Under the firmware section click "Change"
This will open a system pop-up where you can find your downloaded firmware file.
"Flashing" the firmware takes a few minutes, progress can be seen if you open the MatterControl terminal. At the end of the process you will be required to reconnect.