Our choir is doing Mozart's Requiem for the next couple of months, and the alto part is really too high for me; not just a few notes but lots of it. Sometimes I can hit those C's and D's (about 10%), but the effort practicing is really straining my voice. When I don't hit it, sometimes it just comes out as a sqeak and sometimes my control is just poor and I don't hit the *right* note. The longer I try, the worse it gets.

I can choose to sing tenor if I want since we're short of them, but even though I can hit all the notes my voice isn't as strong in that range, so I'd rather stick with alto if I can manage it.

Does anyone know exercises that I can do to target that particular problem and strengthen that upper range without working my voice too hard and making it worse?