Ihave been a professional singer for thirty years.Iagree with alot of what foolestroupe has to say.Ihave had very few problems because I sing from my diaphragm.
Here is an exercise that I use.Istrt at the bottom of my range,low e on the guitar,and I sing an arpeggio,e, gsharp,b, e,then back down b, gsharp low e.then I sing f a c f c a f,and upwards till I cant sing any higher,
I have arange from low e nearly two octaves to c sharp.if you practise this for five minutes every day,you will be able to improve your range.http://www.dickmiles.com