Widening your vocal range, how?

So, I have a naturally deep voice. The thing is that my voice is no good when it comes to low notes but, I can sing well at high notes. But, I can't reach high enough to sing a whole song like that. Like, I'll start off good and then as I need to go higher I can't. Is there an exercise or something I could do that would widen my range and allow me to reach higher notes so I can sing better?