On the left hand menu within dashboard scroll down until you see the icon that resembles a calendar. (labelled Booking)
Double click on booking and the main screen will open. You will now see a list (currently containing one item)
On the right of the screen click edit to open up the editing screen.
You will now see a series of drop down options and below that the actual calendar. Ignore the drop down options as these simply change the appearance of the calendar.
To edit the calendar, you simply have to double click on the date you wish to amend. This will bring up a menu of options to the right of the screen. To make a date appear as available simply click Apply button that is located below the main calendar.
If you wish to change a day to make it unavailable (booked) simply change the drop down option on the right from available to unavailable and press apply button under main calendar.
Finally when you have finished editing the calendar simply click save and your changes will show on the front of the site.