How to upgrade from OH 2.1 to OH 2.2

Hi all,

I do have an OH 2.1 installation (installed with apt get packages).

How can I upgrade to OH 2.2? When I try to run the upgrade script, the system says to me:
pi@openhab2:/usr/share/openhab2 $ sudo runtime/bin/update

#########################################
   openHAB 2.x.x update script       
#########################################
                                     
The script must be called from openHAB's root directory.
Either specify a directory or place this update script in and run from openHAB's root folder.

I think the update script is for manual installations. Everything there script does gets executed automatically by apt-get for you. There is no need to run it separately.