Upgrade zen theme (7.x-3 to 7.x-5.5)? Presuming I have zen-7.x-3.x + a sub-theme, how do I go about uprading to zen-7.x-5.x? Perhaps using drush?

I am in awe of the people who wrote these pages:


https://www.drupal.org/node/219527
https://www.drupal.org/node/1588244
You can run 
drush up zen, it will update the zen theme, but not the subtheme 
Please do a backup before running this command