Navigate to the "Gear" tab/menu at the character screen in the pause menu. Then, press LT + Y to change the hair style and press RT + Y to change the beard style. Note: The changes will reset after dying or reloading the game. Additionally, this was not originally intended to be in the final version of the game. It was a dev tool that was left in the game by accident. They decided to leave it in the game after it was discovered since it is harmless.