i changed the user name and password now i can open the mac put i can't change any thing from system preferences
[Re-Titled by Moderator]
MacBook Air 13″, macOS 10.13
According to the information in that screenshot, "M" is a standard user and no other users are apparent. Are there in fact no Administrator accounts on that Mac?
How did you manage to change the username and password? For future reference the following procedure must be followed: Change the name of your macOS user account and home folder - Apple Support.
MacBook Air opening after changing the user name and password but can't change any thing from System Preferences
