How do I add a new Level (Zone) to Scantronic 9651 Alarm?

I have a Scantronic 9651 alarm fitted with a 9330 remote pad. When installed it had Levels A and B set up; C & D unused. A is entire house alarmed, B is Ground & 1st Floor alarmed and active when set. I want to add a new Level C as house is 3 storey; i.e. when C activated want just Ground Floor to be alarmed allowing 1st & 2nd Floors to be used as we have bedrooms on 1st and 2nd Floor so need just Ground Floor alarmed at night. I know all the zone #'s for the various rooms as the installer put all on the manual. The manual however does not tell you how to set up a new Level.

Can anyone help please?