Hey, I guess what you are looking for is described in the docu.
To make it short, run wget -O - https://raw.githubusercontent.com/laurent22/joplin/dev/Joplin_install_and_update.sh | bash
I saved the bash script in a local folder so I can just run it from there if I need it (But that would of course not always take the up to date version of the script, but I just hope that not a lot is changing in there).
If you want to update to a pre-release on a machine with graphical output you can do this by activating the option as described in here, sadly I haven't found a command to make this change from the command line yet.
Hope I could help.
EDIT: Just found the option to update to pre-release in the bash script: ./joplin_install_and_update.sh --prerelease