How do I replace audio track on Mp4?

[unwired]

Relative Newbie here. I have a video recording of a school musical. The video is saved in Mp4 format and the audio is terrible. The school has a soundboard recording of the audio that is available to me. How can I remove the existing audio track and replace it with a new on? Preferably with Freeware for a Windows XP or Win 7 machine. If a freeware tool isn't available I would like to consider reasonably priced commercial software as this might be the only project I use it for. I have looked into YAMB, but am not sure if it is what I need or not. Any recommendations?

Thanks for your help.

[aedipuss]

you are going to need an editing program. something like vegas studio (they used to have a 30 day free trial so you might not need to buy it). the video and audio will need to be separated(demuxed) which vegas will do for you. add the new audio and then since there is no way they will sync because they were made with different devices you will need to line up the video and new audio properly. delete the old audio and then render out to whatever format you want.

[unwired]

Thanks aedipuss! It looks like Sony still has 30 day trials. I don't mind at all paying for good software, but hate to pay for something only to find freeware a week later that is as good or better for the purpose I need it for. A few years back I used a program to do something similar with a DVD. I think it was called Womble MPEG. It was easy to use and syncing the audio was a snap. But I haven't seen where that is available or suitable for mp4. Are their any other contenders out there that I should consider within a reasonable price range?

[budwzr]

NLE software like Vegas, does all those little nuisance tasks, and all the major editing under one umbrella and eliminates the need for "One Trick Pony" utility apps.