User accounts with 'admin' privileges can delete reservations:
in ReservationDetailPanel->Admin->Delete Reservation:
But of course we recommend using this feature with extreme caution.
Accounting practices will favour invoice runs with continuous numbering. (invoice numbers, reservation references)
We recommending only deleting training reservations.
All other un-wanted reservations should be cancelled - so you see the continuity in your rental sequences.
(e.g. a client who doesn't show up or who cancels)