Deactivating a staff member will allow you to downgrade the cost of your subscription. Doing so however will revoke all access to that user. 

Staff can be managed by going to Staff via the navigation menu.

Now you can select the staff member you would like the delete by clicking on their name. This will display the staff members profile.

To remove them simply click on the "Archive" button at the bottom and confirm by clicking continue. 

Now your subscription will automatically adjust on the next billing cycle.