I can't disable the root user

Question

The OS X says:
"You should disable the root user if you have no further need of it. A root user can modify and delete any file in the system including system files not available to other users. Having an enabled root user on your system eliminates an important layer of security for your system."
In order to disable the root user (System Administrator), the OS X says:
Open Directory Utility, located in the Utilities folder in the Applications folder.
Open Directory Utility
Click the lock to make changes, and then enter an administrator name and password.
Choose Edit > Disable Root User.
The problem is that the option Disable Root User is not displayed. There is only: Enable Root User
Is there any other way for removing the System Administrator from the users log in options, when the computer starts?

Answer 1

Hello Kappy.
There is something weird about this issue.
When I bought the machine, the vendor opened it and initiated the system for the first time at the store.
He typed some random stuff and told me I could change it at home.
Later, when I tried to open Safary, a keychain asking for a password always appeared, but It wouldn't block the access. It was just annoying. I didn't know any password, so I followed the manual to change the original password.
I don't remember exactly what happened, but after initiating the system with the start up disk 1, and setting a password for the "My Account" user, that password still didn't work for unlocking the keychain.
Then I started again with disk 1 and selected the other option: System Administrator (root), setting a password for it.
After that I could operate the access to keychain.
In System Preferences > Accounts display, the only available user is the original one that the vendor typed at the store, and under its name, referring to it, there is: "Admin"
So it seems that there is two Administrators, but the root one is the most powerful, and it always appears in the login options under the name "Other..."
I'm puzzled