Hello.
Booking Calendar Free version does not support editing of bookings.
In this version you need to delete this booking and then create new booking with new details.
Any paid versions of Booking Calendar support of editing bookings in admin panel at Booking Listing page.
Also visitors who submit the booking can edit own booking with secret link, as well. Please check more about this here http://wpbookingcalendar.com/faq/configure-editing-cancel-payment-bookings-for-visitors/
You can check overview of different Booking Calendar versions at this page: http://wpbookingcalendar.com/overview/
Also you can test live demos http://wpbookingcalendar.com/demo/ to be sure in functionality and do not have misunderstanding.
Kind Regards.
