You can use Premiere Elements or a audio editor like Audacity (free).
Place the audio used in the menu on the Premiere Elements Timeline or in a Audacity project. Lower the volume and export a new version of the file. Import that file into your project and replace the old audio clip with the new one.
Using Chuck's recommendation, I find that about -6db to -12db is a good starting point. Be aware that different audio editing programs use slightly different db scales and that all VUE meters are not the same. Experiment until you find the "sweet spot" and jot it down someplace. That will be your starting point for other Audio, however only listening will get you exactly what you want and need.