Did not seem to be a 'How to' title here so I have had to put this under a chords request.

I am learning to play whistles, I often come across tunes which have been written as a melody line. Some of these I have already as notation for a D whistle. But how do you go about re-writing them for a C or F? Also how do you re -write tunes which have been written purely as the melody line for the voice?

Is there a book in print that would help with this?