Loading & unloading Music with Actionscript

I’m trying to add a couple of music files to a CD presentation using actionscript. I know how to load one track but how do I unload a tack when it’s finished and load another after that? Here is the code I have so far:

myMusic = new Sound(myMusic_Mc);
myMusic.loadSound(“Doin It.mp3”);

P.S. using CS3.