Lift the soft palate (back roof of your mouth). Stay relaxed while you do this. If you aren't used to doing this, it will seem at first that you have no control at all. After awhile you will develop the ability to lift. Look in your throat with a mirror and light. See the uvula hanging down? Lifting the soft palate will make the uvula lift up, creating more space for the sound. It helps alot to be able to do this when singing in the top part of your range.

Alice