Xperia M2 upgrade 18.6.A.0.182 is, at the moment of writing this, only available via OTA, which means that if you don't get the notification about the update, you can't get it in any way.
Providing that, and that there're lot's of people currently using Custom Roms, such as OmniRom, CM12.1, SlimLP, Xperia Z5 S.T.Y.L.E., and Gaurav's Deodexed ROMs, they might not be able to get the update. So, if that's your chase, this is for you.
How to install it?
Download the flashable zip, flash it through your preferred recovery and enjoy. As simple as that!
Where can I check quality improvements?
NEW! Download [Stock & NON-Stock-based ROMs]: AndroidFileHost.