How do I change my MacBook Pro 13's login name?

How do I change my MacBook Pro 13's login name? I have an able to add my iPhone and iCloud no problem but when the login name is appears I cannot change it and it has nothing saved onto it I am so confused.... 😐 🤔 is as if the name is just there to log into the computer and nothing is even read is anybody know how I can change your name and do I say things to do in my iCloud I have an android/google person so this is new to me.

[Re-Titled by Moderator]