Use your diaphragm but control it. If you need help doing that, consult a choir director or voice teacher and see if they can help. I've been out of practice for two years, but my diaphragm is getting stronger every day!
btw, your diaphragm is the muscle that allows your lungs to inhale and exhale. when you say "huh" very loud, you'll feel something on your abdomen move, that's your diaphragm. :)