In Order to emergency, change configuration or reset root password. Follow following steps

1. Shutdown the computer
 2. Boot into Recovery Mode --After BIOS load, hold down Shift key to access the grub menu --Once in grub menu, select the entry ending in "(recovery mode)"
 3. From the next menu selected option to enter Root Session
 4. At the root session, execute command mount -o remount,rw / to remount the filesystem as read-write

Then after you can reset the Root password to change the configuration.