Ubiquiti Rocket M2 - M

I have a Rocket M2 with an early version of Aredn firmware.  When I do a sysinfo to determine if it is an XW or XM model I only see an "M."  Is this Rocket too old for an upgrade?  I don't see firmware for the "M" version.  Will any of the other firmware work?

Thanks,

Bob
K6MBY
Sequim, WA