The Rascher book 'top tones' is an excellent resource.
Make sure that you know what the harmonic sounds like before going for it (think trumpet lip slur warm up exercizes). Be sure and think fundamental='oh to ah' s feel inside the mouth, 2st harmonic, 'ah with tongue going toward ihh', 3nd harmonic think 'ihh', 4th and up going toward 'eee'.
That's just a guide, the actual movements are very subtle.
It will take some time.
Make sure that you know what the harmonic sounds like before going for it (think trumpet lip slur warm up exercizes). Be sure and think fundamental='oh to ah' s feel inside the mouth, 2st harmonic, 'ah with tongue going toward ihh', 3nd harmonic think 'ihh', 4th and up going toward 'eee'.
That's just a guide, the actual movements are very subtle.
It will take some time.