Open the WAV editing program of your choice by first clicking "Start." Click on the "All Programs" tab and select the WAV editor from the list.
Click the "Open" button on the WAV editor to browse your hard drive for the WAV file that you want to edit. Click "Open" to add the file to a project for editing. Click on "Effects" and then "Track Volume." Reduce the WAV's volume to taste by way of the level indicator bar.
Click the "Save As" button from the "File" tab. When you are asked, specify the bit depth of the WAV that you are saving and click "Save." Your new WAV file is now stored on your machine with reduced volume.