How to discard a random symbol

Hello,

I have a problem:  I have a keyframe where I must to upload a random series of symbols, and I do it with the script:

var myVar = Math.floor((Math.random()*6)+1);

     var stage = sym.$("Stage");

           var myAni = sym.createChildSymbol("Symbol_" + myVar, "stage");

          myAni.appendTo(stage);

The script works fine, but, at NEXT keyframe I must load another series. The problem is that the symbol loaded in the previous keyframe is still present and the new symbol overlaps it.

How can I unload or discard the previous symbol?

Thanks in advance.

Celine