If you are ticked as a Manager in the 'Manage Leads' role, you will be able to Delete A Test Drive record.  When viewing a Test Drive open the 'MORE' option in the grey action menu and click on the 'Delete' button.

You will be asked to confirm the deletion of the Test Drive record.  Note once deleted the Test Drive Form cannot be retrieved.  If you have integration, or the Test Drive legitimately occurred it is not recommended that you delete any Test Drive Forms.  The function is available to approved users purely to allow them to clean up Test Drives that were never completed, and should be used with caution.  A deleted Test Drive Form will no longer be counted in reporting.