You mean for a "short" period, right?
There are actually a number of ways to do it. The easiest is to use Audio Keyframing.
If you've got one of my books (available on Amazon.com and at the Muvipix store), I explain this with illustrations -- which is much better than I can do on this forum.
But, basically, you move the CTI playhead to the point on your timeline that you'd like to change the audio level. Click on the song or audio clip you want to play quieter. When you do, you'll see a set of white buttons (Keyframing buttons) highlight on the audio track header, left of the timeline.
The center button is the Make Keyframe button. (If you hover your mouse over it, you'll see.) Click on it and a litte white dot will appear at the CTI's position on your audio clip.
Move the CTI and make another keyframe point. By creating these keyframe points and raising and lowering their positions on the clip, you can raise and lower the clip's volume as precise spots -- lowering the volume on a portion of a song, for instance, so that narration can be heard.
It's much easier to explain with pictures.
What version of Premiere Elements are you using?
If it is Premiere Elements 8 or 9, consider using the Smart Mix feature of the program. It can do automatic volume adjusts on the tracks that you mention...say Narration vs Audio 1 or Soundtrack vs Audio 1, but the catcher is that the audio on Audio 1 MUST contain dialog.
If you think that the Smart Mix is worthwhile exploring for your workflow, please let me know, and, if necessary, I will describe its easy application.