In the distro, there is an upgrade directory with a bunch of subdirectories with version names.
To upgrade from 2.1.6 to 2.1.8, you will need to run the 2.1.7/postgresql_2.1.6_to_2.17.sql script first.
Then run the 2.1.8/postgresql_2.1.7_to_2.1.8.sql script.
I would suggest having a complete backup of everything, a fall back plan, and a good plan on
testing your install after doing the upgrade. E.g., check attachments are still there, avatars, poll info, pm's, and the like.
[originally posted on jforum.net by monroe]