geof,

Assuming you mean delete the audio track that is recorded with the video --simply select the clip on the timeline, un-group the audio and video using the little broken chain link icon, then select just the audio and hit [Delete]. If you have the latest version, MEP 2013, you will need to display the audio and video on separate tracks first. This option is available from a right click on the clip drop down menu.

Regards,

Carl