Humans are a sexually reproducing species. That means that humans can be categorized into 2 (two) different sexes called 'male' and 'female'. An individual human's sex is determined at conception, by a specific chromosome pair in their genome. The 2 varieties of the sex chromosomes are designated 'x' and 'y'; females have 2 x chromosomes and males have 1 x and 1 y chromosome. It is not possible to change from one sex to the other, nor would any such procedure be in any way feasible or practical. One's chromosomes are found in each and every cell of one's entire body, so changing from one sex to the other would necessarily entail replacing every single cell. That includes your brain and your bones. There are some people who decide to surgically alter their genitals to superficially resemble the genitals of the other sex. Such procedures do not confer the biological function of the other genitals and always destroy the function of the patient's existing genitals. The justification given for performing these procedures is that they are the best extant treatment for the mental anguish experienced by those who suffer a mental illness known as 'gender dysphoria'. A non-trivial proportion of such patients end up committing suicide anyway.
The deeper one digs into the transgenderism quagmire, the more evidence one finds that it has always been alarmingly baseless and utterly destructive to all involved.