AS3 controlling movieclips

I have a flash project that has several movieclips on the main timeline. One is a movie clip called displayTab that has 5 key frames that highlight graphically what button you have pressed. My buttons are grouped together in another movieclip called CategoryButtons. I’m really stuggling with this simple function in AS3. Previously, in AS2, I think it would have looked something like this:

on(release) {

In AS3, after digging around for a while I came up with:

videoButton.addEventListener(MouseEvent.MOUSE_UP, change_tab);
function change_tab(evt:MouseEvent):void{

I know this is wrong but I’m not sure where to go from here.

Thanks, m