As i understand it you don't change the way you look, you choose your parents and grandparents and then R* takes care of the rest.
Found this quote from Leslie Benzie: "That's not how humans are made in the real world. Normally it involves a man, a woman, and some sexy time." That sexy time is the foundation of your online avatar - instead of breaking down the minutia of your character's appearance, you'll select your parents and grandparents and see what happens. After that, you select a lifestyle (party animal, couch potato, etc) to determine your starting skills.