For those of you who wish to make your Family History presentations private you can update your Prezi accounts for free.
Go to:
http://prezi.com/pricing/edu/
Choose the “Edu Enjoy” option for $0/month.
Use any .edu email address you have. Verify. (Keep in mind the verification email may take a while to be delivered).
Once your .edu address is verified (note: this will not change your log in email) you will now have the option of making your presentations private.