Date

I have a current event set on the site, but the date needs to be changed.  Is there a way to update the date, but keep the existing appointments?

Yes, what you can do is move the slots and appointments. This is done in the Slot Editor. Click on the original date on the calendar on the left hand side and then click on the Move Slots button. This will allow you to move the slots and appointments to a new date. You will have the option to send out an email notifying participants. 

Note that you will want to correct the date you have listed on the Event Setup page, as this does not change when you move the slots.