There's definitely enough good info here but I'll give some extra perspective.
Every human is in the same essential body, configured to different levels like customization sliders or a colour palate.
Different cultures live in different levels of humidity, light, different foods, ways of life, physical activity, etc. This creates physical change over long periods of time. The entire body is a cable system. We represent these cables (think finger tendons running to feet and through head) by elements. They're maintained and mastered(related/controlled) through the organs. These express externally through your face. The face is the body (torso, waist, discluding limbs) and the limbs are your body. The body is the naval. Observe people to see what kind of states they're in (what organs/elements are strong, abused, prominent, etc), what side they angle to.
Another idea is to understand the geometry of males and females. The only "real" difference(of bodies in general) is this geometrical positioning(visualize a square gate or octogate).
What does this mean? Changing the entire body is an act of changing these variables(geometry if you like to think physically). At least this is a denser or more external explanation on how it all works. First you need to satisfy your ego.
Next ask yourself. How can you realistically "break" and manipulate reality to deeper levels. Hopefully you thought the imagination. It's so simple as to be taken for granted. This goes for much more than just shapeshifting.
If we remember the cyclical, sine wave nature of reality we can figure out how this may work. Constant enforcing of this form. Create your body map and overlay it at every chance you get. Anyone who practices astral projection will know this kind of stuff(and may have noticed subtle changes).
High tide is impressing, low tide is allowing and yielding.
This all takes a sturdy posture to support use of the imagination. Strong internal breath as to keep your consciousness flowing and a highly developed creative visualization.
I'd suggest first learning how to visualize properly in 2d,3d, creating Post too long. Click here to view the full text.