Log in to the ITA server Webmin interface.
Go to System > Users and Groups, and click Create a new user.
Enter the Username, define the default Shell (such as /bin/bash), enter a password, etc.
In Group Membership, > Secondary groups, make sure wheel is selected.
Note: Root login (to the server) has been disabled for security reasons, so avoid creating a user name "root". However, if root is the only user created during the software installation, then it can be used to log in to the Webmin interface. You then create a new user as described above.