How can I control my singing voice?

Ok so I know i'm an alto and I've been an alto since the 5th grade (I'm now in 10th btw) and I'm into all the drama club stuff and I also love disney and well all the princesses are mezzo soprano or soprano 1-2 ect.. so i was wondering how i could improve my voice...I know for me singing like Aurora(Sleeping Beauty) or Cinderella is not possible but Belle and Ariel aren't as difficult. any tips? I'd take lessons but right now we can't really afford them and we don't have the time.