By default, only the account holder can create and manage users.
If you want other administrators to create and manage users, you need to permit them to use the account's primary user group in which the users are held.
To grant this permission, go to the Settings folder and select the Sytem settings icon. In system settings, select the User groups icon to see the list of user groups. Select the user group called Account Name Users, where Account Name is the name of your account.
From the user group details page, use the Permissions button to open the user group permissions page.
Add a permission with User or group set to Process client administrators and Permission set to Own users.
Other administrators should now be able to create and maintain users.