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?**