[i]I have 3 buttons, and when they are pressed down, I have them switch their
order using this code[/i]

[b]_root.x+=2;
this.swapDepths(_root.x);[/b]

[i]The flash file is 3 frames, and the 3 buttons are on the first frame. My
problem is that, the last activated button (the one with the highest depth
value) stays on every frame when I switch back and forth, meanwhile I only have
these 3 buttons on the first frame. Why is it staying on screen when it should
disappear when I change frames?[/i]

I created a dummy file which basically is a smaller version of what I have at this moment.

you can use removeMovieClip() to remove movieclips. but then you'll need to
use attachMovie() to get them back on stage.

for your purposes it would be easier to use the _visible property of your
movieclips to control which movieclips are visible on-stage.