To change the name of the Mac, open Sharing in System Preferences.
Enter or change the name of your choice at the space provide:
Don’t mix this Machine Name up with Short Name and Full Name. Machine Name is the name you want to call your Mac and to be shown to others in a network environment.
Short Name and Full Name are the names of the user of the Mac. These two are used to identify who is the user, and to define and create account information on the Mac.