When you set up Ubuntu or Kubuntu or some other Ubuntu-like distro, during the installation process it automatically will add the first user to the sudo group, allowing that user to make changes as the super user (aka root aka administrator if you come from Windows environment) by typing in the related password.
However, if you want to give someone else superuser privileges (please think on it) on your Linux system, you’ll have to give it a specific sudo access.
That is very easy to do. Just run:
user@pc:~$ sudo usermod -G admin username
That’s all!
If you prefer the graphic way of doing things, open System -> Administration -> Users and Groups.
Select the user you want to add to sudo, and click Properties.
Under the User privileges area, check the box “Executing system administration tasks” and you’ll be done.