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

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