It’s actually surprisingly easy! Just download the latest .deb from here to the server. Then install it with:
# dpkg -i <latest.deb>
This by itself does nothing. It just installs the new version in parallel to the old one. All instances must be updated separately with these commands:
# su - <instance_user> $ omd stop $ omd update $ omd start
Now check for new/missing/vanished services and update the agents (it’s not a must, though). Acknowledge all incompatibilities (also not a must) and you’re done!