When I create new events, do I need to delete all the registrants?…is there an easy way to get rid of these so the new classes don’t show people already registered?
The new class won't show old registrants. Maybe the reason is because you have multiple events with the same title ? Could you please go to Events Booking -> Configuration, look at SEF router settings tab, find the config option Insert Event ID, set it to yes and check it again !