We do not recommend deleting a Staff Member/User that has left, since deleting a Staff Member/User record deletes all their Time sheet entries and Appointments from the system, and this process cannot be undone.
Instead, open the staff member record under Settings > Staff Members and place a tick in the check box, "Archive this Employee" at the bottom left of the screen. All the Staff Member/User's history will be maintained.
We recommend that prior to archiving the Staff Member/User, you reassign any future dated appointments, for that Staff Member/User, to an active Staff Member/User.
Once the employee record has been archived, then go to Settings > Subscriptions & Billing and adjust the user numbers there accordingly, enter your Billing Information including your Credit Card and then click on the "Update Subscription" button in the bottom left hand corner