Run sudo
Run sudo -i. This will give you an interactive root shell at your current directory. 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.
Use the su (substitute user) command to get a root shell. This is effectively the same as usingsudo -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.