removing a class

Hi all - this might be the silliest question around, but I just can't seem
to figure it out.

I've created a highlighter tool, that allows the user to highlight text on
the stage. I'm initializing the external class by using:

import highlighter;
var myhighlighter:highlighter = new highlighter();

But when the user goes to the next frame, I can't figure out how to turn the
thing off. How can I delete the myhighlighter variable?

I've tried:

delete myhighlighter

and

myhighlighter=null;

But nothing has worked. I know this has got to be easy, but I just can't
seem to figure it out. Thanks for your help.