Hi Tika,
the Version could be located left-Top:
raw or enterprise
first backup like here:
https://checkmk.de/cms_omd_basics.html
Point 9
- then update of the CMK
then Debian
but if i see the Information from your system
it`s an old OMD Installation
IMHO - the best way is to setup a new Server with a clean installation
Greets