Movie Clip fading problem

programming flash
1

Hello

I have just started using Flash and have come across a problem.
That being, I have no Idea how to change the Movie Clip using the directional keys.

The Program I am wring is just to change between Movie Clips when pressing one of the directional buttons, but every thing I have tried has either just removed all of the movie clips or shown both.

The code I am using is this but instead of removing the “Cloud Left” Clip it just shows “Cloud Right” and “Cloud Left” at the same time

onClipEvent (load) {
walkSpeed = 5;
}

onClipEvent (enterFrame) {

    if (Key.isDown(key.RIGHT)) {
      
       this.removeMovieClip("Cloud Left");
       this.attachMovie("Cloud Right");
        _x+= walkSpeed;
     }

}