To update a Word document: open it in MS Word, do the necessary changes and save it again.
Updating a downloaded mp3-file to make it sound more like you prefer is much more difficult, alas.
So - not unexpectedly, maybe - it's dependent on the file how to update it.
Now add some detail so that smart CNET users (like you!) can answer. If you're lucky, a CNET editor might choose your topic for a How To article or video.