Upgrades within UBB.threads utilize the built in upgrade utility for simple upgrades; when a site goes years without updates (many versions to pass) there will be times that you'll need to do an incremental update to "catch up", these are relatively rare but do occur (such as adding the Global Moderators feature in v7.3) and are as easy as upgrading to the "stopgap" version before upgrading to the latest build.
You can find a list of developer notes with each version and the release date on the wiki at UBBWiki
(UBB.threads Changelog Index
) or in the Changelog Discussions
There are numerous modifications available at UBBDev
(the home of the team contracted for development of the UBB.threads product) and I offer several premium/paid modifications and themes at VNC Web Services