Changing the user password on a Raspberry Pi

To change your password on a Raspberry Pi, use the passwd command:

robert@rpi $ passwd
Changing password for robert.
(current) UNIX password: 
Enter new UNIX password: 
Retype new UNIX password: 

passwd: password updated successfully

You will be asked for your current password, then to enter your new password twice to make sure you don't make a mistake.