To update a working version of show just extract an archive named show-update-* inside the current installed version.tgz. The following files/dir will remain unchanged 
-inc/config.inc.php
-admin/.htaccess
-sh/precache.sh
-medias
-cache
This can cause problem in case of important changes in these files.
The video thumbnails will need to be regenerated because the overlay image will be updated.