To replace the normal text password login with ssh public/private key pair....
Generate a pair at home (creates RSA based key pair)
ssh-keygen -t rsa
Enter in a passphrase when it asks.
upload the .pub key to the server
sftp root@<server address>
lcd /home/<your login>/.ssh
Login to the server normally as root.
Goto the .ssh directory
Append the public key to the authorized_keys
ssh root@<server address>
cat id_rsa.pub >> authorized_keys
Then check that /etc/ssh/sshd_config has...
... in it
Restart the ssh server
Try logging in again as root and you should be prompted for passphrase to your ssh key.
ssh -v root@<server address>
to diagnose problems