By default, Ubuntu locks the root account in an effort to force the user to use sudo rather than logging in as root https://help.ubuntu.com/community/RootSudo
That said, you don't need to login as root to be able to change file permissions. If you login with your user level account you can change file permissions via the command line with sudo. If you open a terminal window you can use
sudo chmod <permissions> <filename>
to change the permissions of a file or directory. Information on how to set the permissions can be found by typing "man chmod". If you need to change user or group ownership you can run the following command
chown user:group <filename>
Further information on the chown command can be found by typing "man chown".