ActionScript 3 :: How To Remove Or Update BitmapData For New Level

I'm making a maze game. The character can't walk through the walls of the maze (because of a collition detection between the bitmapdata from the character and the bmd from the walls). When the character arrives at a door, the next level/frame should appear with a new maze (new bounds). For the next level (next frame), I made a new maze with different walls. But the bitmapdata from the first maze is still 'active'.

So even though there's a new maze, the bitmapdata from the previous walls is invisible but still drawn on the stage. My question to you is: I want to change the bounds/maze every frame, how can I remove the previous bitmapdata so the character won't walk through the bounds of the next maze? Or is it possible to make an array from the different 'bounds'?

stop();
var isRight:Boolean=false;
var isLeft:Boolean=false;
var isUp:Boolean=false;
var isDown:Boolean=false;
var speed:int = 10;
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