Confussed?

I am making a menu type thing where the user presses a button and the movie clip with the buttons contained on it moves down

on (press) {

this.port_1.film_port._y+=5;
trace(this.port_1.film_port._y);

}

_root–>port_1–>film_port is the structure of the movie clips

I cant see why this doesnt move the film_port movie clip 5?

if someone can explain then this would really help.