If you are using amplification and mikes, try singing much more quietly than usual and let the technology take the strain. This can give you access to a wider range then when you are trying to sing everything at concert pitch and concert volume unamplified. You will need to take care with your pitching, though, as too much amplification can make one sing a little sharp. Find any "break" points in your range and practice singing through them without glitches - tricky, but can be learned.

If you are not using amplification follow the tips from the others above, or find yourself an amenable singing coach (the right one can be worth their weight in gold), and keep practicing.

Good luck,

Gray D