Changing chords

Question: "The movement I'm doing now, from what I understood, is that if I play a chord the whole hand, wrist, arm, back is involved. That way there is not need to squeeze thumb and fingers. But if I want to change chords, when releasing from the previous chord do I bring the whole gesture back - so there is no movement from the fingers itself - in order to release the strings?"
Answer: To change chords you can often go through a "neutral" position, where the hand and fingers are totally relaxed, which I think is what you are describing. Players with a lot of "stamina" - or the ability to play long pieces, have found hundreds of places to momentarily rest the hand and fingers within the music.

If you relax, the hand will fall away from the strings easily, due to gravity.

Chords, and how to change chords quickly is explored thoroughly in my book: Bach's Guitar: Master Chords and Unlock Your Right Hand