How do I disable remote SSH login as root from a server?

I assume you meant logging in over SSH? Put the following line to /etc/ssh/sshd_config:

PermitRootLogin no

If you want to deny certain users from logging in, put this in the configuration file:

DenyUsers root

This takes the blacklisting approach. Whitelisting is generally preferable. If your company needs to allow the rob and admin users log in on the server, use the following configuration directive:

AllowUsers rob admin

After making configuration file changes, restart the ssh service using the command:

sudo service ssh restart

See also the manual page.

Edit the file /etc/ssh/sshd_config, look for

PermitRootLogin

and set it to no.

The default configuration is for the root account to be locked so you can not log in as root remotely. You don't have to do anything else, unless you also want to make sure that you can not log in as root remotely by using an RSA key. Of course, if you don't want to do that, then just don't set up a root key.