3
Greetings,
Some of the modules have an "update module" link. This seems to be the case for "Smartfactory" modules. Otherwise, it seems that the updates are generally posted first on the developers own site. Generally, the developers site is mentioned in the forums or under "comments" section for that particuluar module on this site. Once you find them all, make a list so that you don't have to look them up again.
Good Luck!