The Drupal Shell is an amazing tool if you maintain Drupal web sites and you have shell access to the server, where the Drupal site is hosted. This is also an unvaluable tool if you develop i in Drupal.
Updating drush: composer global update drush/drush
Manual install: http://docs.drush.org/en/8.x/install/
Check latest drush version: https://github.com/drush-ops/drush/releases/