Joe is telling the truth. Max amount of time it takes (with mistakes included, forgotten passwords etc.) to upgrade system is 30 minutes. Thanks for the instructions Joe. THey helped me upgrade a VPS to 1.9.3... now to pump some calls...
FYI, here's the link where Joe describes updating:
http://forum.asterisk2billing.org/viewtopic.php?f=33&t=8660P.S - the update that I did was from 1.8.5 to 1.9.3. Mind you, I didn't do any changes at all to the system in terms of web interfaces, so in that case, your system should not break if you do the upgrade the way Joe suggests.