Help with my game

Hi, i’m kind of new to flash and I started creating a game and i’ve gotten to the point where my game can: shoot, move char., kill enemy and add to score, once lives = 0 then game over, and multiple enemies that shoot.

Ok, my problem now is that i’m trying to get it so that once my score is over a certain amount then increase the number of enemies, and i’m using this code now to control how many enemies are on the screen at once:

}
var numEnemy = 2;
function Enemys() {
    for (j=2; j<=numEnemy; j++) {
    var name = "enemy"+j;
    _root.enemy1.duplicateMovieClip(name, j);
}

I can change ‘numEnemy =’ to any number and thats how many enemies will be on the screen at once. Then I used this code to increase that number once my score was over 250:

}
if (_root.score >= 250) {
    numEnemy = 3;

but for some reason this just doesn’t work… Can anyone tell me why or link me to a tutorial on how to create levels in a game?

Thanks.