To be able to make a massive cancellation of reservations we go to:
Tools → Bookings → Cancellation of Bookings/Bookings deletion
We will open a window with the list of all reservations. If we want to make a massive cancellation we will click on the option "Select all" as shown in the image.
When we see that a tick has appeared 
on the left side to select, we will click on the "Deselect Selected" button at the bottom of the screen.
We also have additional reservation search options.
To see them, we must press:
As we can verify, we can search reservations by the name of the client, by filtering dates from to and by filtering hours from/to. We can also specify the status of either, by the type of reservation, by the resource or track of the reservation or by the center.
For example, if we want to cancel all reservations on Court 8 we will do the following:
All the reservations will be listed.
Another option to delete reservations, would be from the table of reservations. One by one, or scheduled reservations. Canceling only the current, from this series or delete directly the entire programmed series.