Someone left. How do I remove them?
Switch them off in Setup → Team; their history stays.
In Setup → Team, edit the person, untick Still working here and press Save. They can no longer sign in and are not offered for new bookings. Their past cleans, photos and notes stay in your records.
Check the calendar for future visits still assigned to them and give those to someone else. You cannot switch off or demote your own admin login.