You can easily cancel or reschedule participants who have either been invited or confirmed by looking for a red cancel button after clicking on their interview spot from Scheduling >> Calendar. You'll notice the layer will look different depending on if they are confirmed (top image below) or if they have only been invited (bottom image below).
To reschedule, simply drag the confirmed time to a new time during that week. At this time we don't allow rescheduling to a new week.
Make sure you've customized the cancel email under scheduling >> emails, which looks like below: