When singing in your upper range, make sure not to constrict by placing the sound in your throat. Vocal tension will affect the quality of your sound, make singing more difficult than it should be, and most of all can eventually cause damage to the vocal folds. When singing in the upper register, keep the throat nice and open, and most of all, allow the throat to relax. This will enhance your sound, and is one great way to ensure vocal health. If any of this sounds foreign to you, please seek out a good vocal coach in your area to help.