hi Ken,
That is possible for some small degree ("small" means up to +/- 2 semitones), by simply changing the speed of the audio file. But if you need more than 2 semitones, then this doesn't work well, because the change of tempo becomes noticeable. Also keep in mind, that this technique changes complete sound, including drums. There are audio editors which can change the key without changing the tempo, but again: if we need more than about 2 semitones difference, then we can expect sound distortion.
In short: I think it's better to re-record the song as midi file -that way you can easily modify it later if necessary.
Bogdan