To change your account name and model's appearance, please click your avatar on the top left side of the main page or on the farthest right side of the bottom menu bar. You will see your account information, including your name, and a pencil icon will be beside it. You should click that to enter a new name and save it. It will be updated right away.
As for the model, you can click the clothes icon on the top right corner of the screen, below your balance indicator. There you will have the option to choose the desired clothes, make-up, and hair.