User Management in NorthStar is all handled from within the main NorthStar user interface. To access to User Management section login to NorthStar and the admin user (or any other user with the Add User permission) and click the "Manage Users" link on the leftmost menu.
The permissions systems in NorthStar is split into 4 basic units (add/edit/delete/view) for each type of object (Networks/Owners/Devices/Locations/Users/Templates/Fields/Regex's). When assigning permissions to a user you should be careful to only assign permissions that the user actually needs. For example, if a user is only supposed to update contact information for a particular Owner they should only have the 'Update Owner' permission set along with any other permissions for other objects.
A lot of care should be taken when assigning the 'Delete' privilege to anyone because delete actions within NorthStar will not only delete the specific object, but also objects that are referencing it. An example of this is deleted a Device object will not only delete the specific Device object, but also the Network objects that are assigned to that Device.
For more information on changing user permissions please refer to the 'User Management' section