How can I edit the audio of a Kodak digital camera video file?

I recently took a video of my family sitting around singing hymns.
Years ago we were a family of singers, but that was years ago. I
wanted to make it a dvd for my Pawpaw but we sound horrible. It's
embarrassing because that's not what we sound like. What program can I
use just to get us together on pitch?

He's led his family of singers for over 80 years and given we will
never be just sitting around singing again I'd like for this one to
sound at least decent.