Part extracting problems

I am in my school's jazz ensemble, and we're playing a version of Don't stop believin'. I didn't like it, so I borrowed the score from my teacher and set out to write a better version. I just finished it, and it sounds great. (At least to me) But, when I go to extract the parts, the staves remain the same size as they are in the score; way to small to use for a part. The catch is that I don't know how to turn the staves into a legible size again. Anyone know how?