I`m asking that cos the flute shakes when I move from C to another note, the some of the thumb strength lies on the top of the flute

it`s just somehting you have to work on. try practicing moving from b natural to c, slowly until you can carry the same sound, volume and security over from the b to c.

You need to be using the side of your left index finger correctly, have your thumb in the correct place, be using your right little finger appropriately, be generally holding your flute correctly, and play with only gentle pressure of the flute against your chin/lip. Perhps you need a teacher.

Other than that, it just comes with practice, as you fine tune the extent to which you are using the muscles of all those parts mentioned above.