Set a new password for the root user.
sudo passwdNow open for editing ssh daemon's config file /etc/ssh/sshd_config.
Set PermitRootLogin value to yes to enable logging is as root.
PermitRootLogin yes
Also check value of PasswordAuthentication. If it is set to no then set to yes for security reasons.
PasswordAuthentication yes
Then restart ssh service:
service ssh restartNow you can log in to your server as root user.
ssh root@domain.com