Change Apple ID
How do you change the Apple ID on a MacBook Air
MacBook Air
What exactly are you trying to do? Do you want to do a name change to the existing ID? Are you selling/giving the computer to someone else? If you are trying to sign out of the existing ID, use the 2nd link I posted as a guide.
Note the restrictions in the article.
What to do after you change your Apple ID or password - Apple Support I suggest doing this before you change your Apple ID or password.