Changing my password

From Linux 101, The beginner's guide to all things Linux.

If you would like to change your current user's password, enter the following command into a terminal (Applications->Accessories->Terminal, although this varies with Window Managers):

passwd

Then type you current password, and type you new password twice. If you are using Ubuntu, this password will be used for all administrative purposes. To change the password of another user (if you have permission to do so) you would simply append the name of that user to passwd as a command line argument.

passwd randomuser