The super user with unrestricted access to all system resources and files is the user named "root". You will need to log in as user root to add new users to your Linux box

 How can I change my root password

$su -l root

[root@H]# passwd

Changing password for user root.

New UNIX password: 

Retype new UNIX password: 

passwd: all authentication tokens updated successfully.

 Type passwd command as follows

# passwdOutput:

Changing password for user root.
New UNIX password: 
Retype new UNIX password: 
passwd: all authentication tokens updated successfully.