change root user in ubuntu

1. Run sudo <command> and type in your login password, if prompted, to run only that instance of the command as root. Next time you run another or the same command without the sudo prefix, you will not have root access.
2. Run sudo -i. This will give you an interactive root shell. Note that the $ at the end of your prompt has changed to a #, indicating that you have root access. From here you can run any sequence of commands as root, or run the command exit to leave the root shell.
3. Use the su (substitute user) command to get a root shell. This is effectively the same as using sudo -i. Note that when you use this command it will ask for the root password and not your login password. These are not the same. You may have to set or change the root password by running sudo passwd root first.
4. Run sudo -s. This gives you root access, but maintains your current SHELL. Shell specific settings, including your current directory, are preserved. For instance if you use bash (Ubuntu's default shell), aliases (and any other settings from ~/.bashrc) are kept when you switch to the root user.
5. exit root user use in terminal type exit . Or you can simply press CTRL+D.