How to 'do-release-upgrade' from 16.04 to 18.04 remotely using PuTTY?

[Bo Berglund]

I have an Ubuntu Server 16.04.6 LTS. It is used as a web server,
OpenVPN server and Subversion backup server.
It is headless on Intel CPU (64 bit) hardware without both display and
keyboard. I manage it entirely via PuTTY from my Windows7 PC.
No graphical interface is installed on this server.

Now on logon via PuTTY it displays this:

New release '18.04.2 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

When I google this command I get to pages saying it cannot be done
remotely via SSH, is this true?

Is there no way to upgrade the system to the next LTS version except
by hooking up a keyboard and monitor to it (Only VGA video
available....)???


-- 
Bo Berglund
Developer in Sweden