In Windows 7 you can change the password of the current username using the command prompt along with the net command which controls most of the system through different command strings.
Go to Start and type "cmd". Right click the found item on the list and run it as Administrator. After the Command Prompt is open, type net user to list the users on your computer then select for example: **net user testuser * ** and you will be prompted to select a new password. Type it twice and the password will be changed. If you are a computer Administrator, you can change passwords to other accounts using this way.