In the administration area, in the section Departments, you have the option of creating, editing and archiving them. Here you can access the department overview.
If you have selected a department, you can see which users have access to it and remove access via [-]. You can assign access to this department in the settings of the users. You can revise all the settings of the department via [Edit].
If you want to archive a department, click on "Edit" in the department.