Hello daniellench,
You can't change a username.
You may only delete it.
With that said;
To create a new user:
1) open a terminal
2) log to your Zentyal server using SSH
3) create the user using this command:
sudo useradd <username> admin
e.g.
sudo useradd daniellench admin
ref:
https://help.ubuntu.com/community/AddUsersHowtoIn order to change a password (from the shell)
1) log to your Zentyal server using SSH
2) change the password of a user
sudo passwd <username>
e.g.
sudo passwd daniellench
In order to delete a user (from the shell)
1) log to your Zentyal server using SSH
2) delete a user by typing
sudo deluser <username>
e.g.
sudo deluser daniellench
Nota Bene
1 You may change your own password by simply typing "passwd" (no need to sudo or append the username)
2 You may create unlimited admin this way BUT consider the fact that only
1 admin at a time can access the admin panel.
3 I do prefer using the CLI since it is faster. Still, you may change the password of your admin user through the Zentyal interface.
Best,
Marcus