Stim and Nigel, Braken has asked a perfectly reasonable question and your best response is to bemoan him... He won't after all lose the originals by experimenting with a bit of editing.

Anyway, is there a free way to edit the notes? Yes. Audacity would be the obvious choice of program to use. Would it be easy to do? It's difficult to say without knowing exactly what you mean by 'bum notes' and the complexity of the piece.

A couple of suggestions:

If the bum notes are a single wrong notes, you could try to use Audacity's 'Change Pitch' function. (this won't work if it's part of a chord with other right notes as it will change them too)

Alternatively, and probably a better option, if the tune has repeating phrases as nealy all do, copy and replace the mistake with an instance with one when it was well played.

Audacity does have a learning curve, but it's not that steep. My suggestions basically involve highlighting the relevant part and then proceeding as above.

Hope this helps,

Ed