I need to learn to sing a "Soprano C". Any suggestions on how to widen my range enough to comfortably sing it?

Just in case you don't know (or im calling it by the wrong name =] ).....a soprano c is the c 2 octaves above middle c. I need to learn it for a solo in my choir cl. My teacher gave me the solo, but if i cant sing it, were just going to drop it. I can sing it but it doesnt sound very pretty and it sounds very strained. Anyone have any suggestions or vocal exercises i can do to improve it? It'd be greatly appreciated =)