Best way to determine which firmware you’ll need is to print a self-test ticket and look at the firmware it currently has.
“G” version firmware may be downloaded to a printer that has “G” version or lower (F,E,D,C,B or A).
Download Version G“M” version firmware can only be downloaded to a printer that has “M” version already.
Download Version M“N” version firmware can only be downloaded to a printer that has “N” version already.\
Download Verison N