I've lost administrator access and /var/db/.AppleSetupDone is read only I have lost administrator access  after trying to change my username in system preferences and restarting.

I have followed the directions by rebooting in Single user mode, ⌘S and typing the following commands:

/sbin/fsck -fy    

/sbin/mount -uw /  

rm /var/db/.applesetupdone


It then asks if I want to override rm /var/db/.applesetupdone and if I then type "YES" it says that it is a read only file and nothing happens.

I have also tried typing rm /var/db/.applesetupdone in terminal and again it asks me if I want to override, and again answering YES I get the reply Permission denied:  

override r--------  root/wheel for /var/db/.applesetupdone? YES

rm: /var/db/.applesetupdone: Permission denied


I am using MacOS High Sierra Version 10.13.4  

How do I remove applesetupdone or get administrator privileges back?
You can run the command as superuser (explanation on wikipedia)

Either run

sudo rm /var/db/.applesetupdone


or

su


to log in as super user and then regularly run the commands.