Please read: http://galleryproject.org/gallery_3_0_5

Upgrading Gallery 3 is really easy!
After webapp-config -U ...  browse to:
  http://${VHOST_HOSTNAME}/${VHOST_APPDIR}/index.php/upgrader
or at a shell prompt: 
  php index.php upgrade 

For more detailed upgrade instructions, please refer to the
Gallery 3 User Guide at http://codex.galleryproject.org/Gallery3:User_guide:Gallery3:Installing_and_upgrading#Upgrading