This tutorial will help how to change the password in ubuntu.For changing the password follow the follow the steps bellow:

Step 1: Select recovery mode the second boot option in your GNU GRUB console.

Step 2: In Recovery Menu window select option Drop to root shell prompt and press Enter.

Step 3: If one forgets the username use the following command to know the username

root@domain:~$ ls /home  (where l => small L)

Step 4: To reset the password type the following command

root@domain:~$ passwd username

Step 5: You are now prompted for a new password. Type the new password

Step 6 : If you don't get any output such as

    Sorry , try again 

then the password acceptance process is under process

Step 7 : After the password is reset type exit on the console to return to the recovery menu.

Step 8: Select Resume normal boot option in Recovery Menu window and click ok.

Step 9: Reboot the system and select option Ubuntu , with Linux.. in the GNU GRUB console.

For more information click the link below:

http://www.psychocats.net/ubuntu/resetpassword