By default SSH Login for Root is disabled in Ubuntu, but it is convenient to directly login via SSH as root, so here is how it can be done:
Login to your server, use
"su -" to gain root access
Then
vi /etc/ssh/sshd_config
OR
nano /etc/ssh/sshd_config
depending upon your text editor.
Now add following line to it:
PermitRootLogin yes
Now restart SSHD:
systemctl restart sshd
or
service sshd restart