First, browse to the navigation on the left hand side of your Pinpoint Admin Screen and select 'Organisation' under the 'Company' section.
Locate your departments by going to the 'Organisation' page:
Then you may need to scroll down and the 'Departments' will be shown in either of the below locations (depending on your screen size):
Click 'Edit' on the Department that you would like to change:
Edit the information as desired and then click 'Save' to complete the edit: