How to remove a bitmap

I am very new to ActionScript programming, and I am using AS 3.0. I am attempting to create a drawing that constantly needs to be updated. The drawing is a graph based on arbitrary, constantly changing, data points. Each frame however needs to be redrawn with a new bitmap. How do I remove the old bitmap before I display the new one ? I have tried using remove child, but when I do, nothing at all is displayed.

Any help at all is greatly appreciated.