Murray, I have been keeping track of singing threads and put them together in one - click here - threads on the singing Voice.
There are links in that thread to sites on vocal health, warming up your voice, and many discussions on the subject including expanding your range.

In general, you have to realize that we are each born with unique vocal cords (now referred to as vocal folds) that will have potential range, quality of tone, and the unique sound that is our voice. The best way to expand your range is to find a good voice teacher and spend the time learning how to use your voice to its full potential. That includes learning how to control your breath, gradually singing higher and lower until you can "hit" those notes, and learning how to lift the soft palate in the back of your mouth, how to relax muscles, how to place your tongue, and more. This is best done one-on-one with a GOOD teacher, a person who has extensive experience themselves in what singing entails, not someone who will approach you with a template and try to make your voice fit into it. Find someone who will teach you from the point you are at with your voice and help you form your instrument into what it can potentially be.

If you can't take voice lessons, some suggestions provided here already will help you. But, whether you are doing these things correctly can only be determined by a good teacher or another good singer LISTENING to what you are doing and telling you whether or not you are doing the techniques correctly. This isn't really something that can be learned from a book or tape. Someone else has to listen to you and show you what to do.

Lifting the soft palate, relaxing, having enough breath and control over the breath, gradually stretching your range, being able to float the tone on air (breath) rather than forcing it.... Think of the muscles in the floor of your abdomen, and pull them down when you breath in. Hold those muscles down as long as possible as you sing a note. Think of your lungs as a bagpipe and that you are creating as much space in your torso as possible to fill them with air by pulling downward with the floor of your abdomen. Pulling your other organs lower and holding them down, then slowly controlling the release of air from your lungs is what is meant by breathing from the diaphragm. Funny how people repeat that phrase about the diaphragm, but people don't usually explain what it means.

Don't visualize HIGH as UP THERE or a note ON TOP when you are trying to sing higher notes. It will only intimidate and tense you up. Think of PULLING DOWN with the muscles on the floor of your abdomen, then gently sing a high note, thinking -pull down, not jump up! Also, realize that your vocal chords are only moving to make a larger or smaller space to make the low or high notes. It isn't an "UP THERE" location at all. I think because we visualize notes on sheet music at the top or high keys on a piano, and use the word "high", many of us think of those notes of the as UP, and that can cause tension. Think of the cords in your throat instead, becoming stretched horizontally to a smaller opening to make that pitch. Think of the breath being controlled with support of the muscles that hold your internal organs. Think of the bones in your head and the spaces in your sinuses as the vibration sounding board. Some singers when they are learning this visualize a spot between their eyes or above the top of their head to feel the resonance of the pitch while they sing it. Singing exercises and songs every day that take you into higher and higher pitch will help you to reach your potential range.

hope this helps

Alice Flynn