Drush

To use drush you have to be somewhere in the site directory as the siteuser (ie not root!)

Download a module

drush dl modulename

Enable a module (and download and enable all dependencies!) after download

drush en modulename

Update a specific module

drush pm-update modulename

or

drush up modulename

Update everything at once

drush up

Update just the core and not the modules also (handy if you want to do it step by step!)

drush up drupal