There are 3 ways to reschedule your appointment, and 3 methods to enable/disable your notifications sent to clients.
1) Changing the time
To change the time of the appointment enter the Edit Appointment screen
2) Edit the appointment details
When you are finished editing the appointment details, when you save you will be prompted to enable or disable the notifications.
3) Changing the date of the appointment
Access the change date window the same as changing the time but when changing the date you will be immediately prompted to send notifications once the date is selected.
The last scenario is when you drag & drop an appointment to a new time or date on the calendar. When you change an appointment in this manner you will have a pop-up screen prompt you to send a notification and update the appointment.