On any given Drupal site, at least several add-on modules and themes will be used.
It is important to keep those up to date, too.
On any of the sites, we can check at a glance whether or not there are newer modules available by going to Administration | Reports | Available updates.
The process for updating modules and themes is largely the same as performing a
site update:
1. Put all of the sites in maintenance mode.
2. Download all of the modules and themes that you want to update.
3. Unpack them and put them into their appropriate locations. We have been placing our contributed modules in sites/all/modules/contrib/ and our themes in sites/all/themes/.
4. Run update.php as we did before.
5. Bring all of the sites back out of maintenance mode.
Often the updates can be done from the command line, should you so desire, with Drush. To update the code for all of your modules and themes, you can run drush updatecode, and then for each site run drush updatedb. The only downside to using Drush for this task is that module owners do not always test with Drush, and (sometimes spurious) error messages may occur during a Drush update that would not otherwise arise during a browser-based update.