loadMovie to target_mc not unloading previous SWF

programming flash
1

My previous SWF is not unloading, the subSWFs are stacking on top of each other .

I tried the following but I definitely see the previous SWF underneath.:

fourthR_mc.onRelease = function() 
{
 target_mc.unloadMovie();
 
target_mc.loadMovie("rightChair4.swf");
 
}