Play simple songs but take it up a third and then when you're comfortable with that, go a little higher. Often people can't play high because they worry and stress about hitting the note. Don't hit the note, play the note. John Thomas has an excellent DVD called the secrets of Trumpet playing (I think that's the name) that may be able to help with this. Also, for your age that's an impressive range!!!! Listen to a lot of Maynard, Eric Myiashiro, Bergeron, Sandoval and you'll have what high notes should sound like in your head. Find one of these guys you really like and imitate them. That's how we learn. First we're inspired, then we imitate. After a period of time, (hopefully)we begin to develop our own uniqueness.
Remember!!! high notes arn't everything. Be sure to play the entire range and when your sound starts to suck, quit playing. Good Luck