A scheduled audit can only be deleted if it has not been started.

To view all scheduled audits select Audits from the left hand menu. 

Filter and Click on the audit you wish to delete.

Click Delete audit from the top of the screen.

This audit has now been deleted from the audit schedule. All subsequently recurring audits will also no longer automatically schedule.

If an audit has been started, the audit cannot be deleted, instead you would abandon the audit. See Abandoning an Audit for more details.