Start by selecting the Audio Workspace
Select the Audio TRACK Mixer tab in the Audio panel.
If you don't see it, use the little double arrows to navigate to the audio track mixer tab.
Use the slider to lower the overall volume of a given track.
Bring it all the way down to completely remove the audio or press the M on the track to Mute it.
There is also a slider for the overall mix volume that you can adjust.
Select the Audio CLIP Mixer tab in the Audio panel.
If you don't see it, use the little double arrows to navigate to the audio clip mixer tab.
Use the slider to lower the overall volume of a given clip.
Bring it all the way down to completely remove the audio.
Expand your Audio track horizontally and vertically.
Use your zoom handles on the right and below your tracks.
There is a line in the middle of your audio. This line represents the volume (in db) of your clip. Grab the line and drag it up to make your clip louder, or down for quieter.
With the Pen tool, draw keyframe points along the volume line.
Drag a section down (or up) to increase or decrease the volume of a word, phrase or section.
Hold SHIFT to snap it to a decibel level.