A person who changes their sex is, as I get it, a person who does not want the body, or parts of it, they were born with, because they do not believe these parts are appropriate for the gender with which they personally identify. It's not about who you have sex with, but about how you wish to view yourself (and wish others to view you).
It's complicated and I don't understand it well, but there's your gist.
It's complicated and I don't understand it well, but there's your gist.