Incrementing question

Flash 8
AS 2

Im very new to AS and I hope this don’t seem stupid.

All I want to do is double the height of an object every time its clicked.
Here is what I have so far and it works, but only one time. I want to be able to click it again and have it double again.

function changeBox(){
myBonus._height = 19 * 2;
}
myBox.onPress = changeBox;

Can you guys help?

Thanks!