To allow root login through ssh. Edit the file /etc/ssh/sshd_config.
As shown below, comment out #PermitRootLogin without-password and add PermitRootLogin yes.
Once the file is saved, you will need to restart the ssh daemon in order for the changes to take affect using the command below.
service ssh restart
After the ssh service is restarted, you should now be able to login through ssh using your root account and password.