It's the same in the Home Patrol. Connect the scanner as described above, choosing "Mass Storage", then use Windows Explorer to find the HP-1 among the removable drives listed. Click on the drive.I don't have the HP-1, but I can offer a potential idea with what I've found with the 536.
Connect the scanner to a computer. Use the computer's Windows Explorer to look at the scanner's files - the scanner shows up as a Removable Drive.
Somewhere in those files there is a folder called Audio. In the 536 there are two sub-folders, inner_rec and user_rec. Opening up the folder(s) will reveal the recorded audio files. I can then use the Windows Explorer to highlight and delete those files I wish to discard.