Can you lower vocals on a prerecorded song in Garageband?

Hey all,

I have some old band practice tapes from the 1990's that I've converted from cassette tape to MP3. These are unrefined basement tapes, but the band was sounding pretty good. The guy that was running the sound at the time had the lead vocal turned up too loud and it's a bit distorted. Is there any way in Garageband to single the vocals out and adjust them without affecting the rest of the recording, as everything but the vocals is sounding fine. I don't have alot of experience with Garageband, and I might be asking the impossible here, but was just curious if this could in anyway be done. I just don't want to affect the volume of the band. Let me know the details if this is do-able.

Thanks!