Add / delete / change: https://help.oclc.org/WorldShare/WorldShare_Admin/User_Management/User_Management
Assigning roles and role definitions: https://help.oclc.org/WorldShare/WorldShare_Admin/User_Management/How_to_assign_roles_to_users
Under "Service Configuration" (which is easiest to access in the lower right link stack on our ILL page in the WMS):