How to Change the Windows 7 Administrator Password
Windows 7 requires an administrative password to authorize changes to the system by standard user accounts. Changing this password requires altering an administrative user account on the system. You can change the password for any administrator account provided that you are currently logged in as an administrator. Windows includes a password reset utility that allows you to quickly make changes to any account password.
Press the Windows logo key and the R key to open the "Run..." menu.
Type "control userpasswords2" without quotation marks and click "Open."
Click the name of the administrative account for which you want to change the password from the list of users.
Click "Reset Password..." and enter the new password twice.
Select "OK" to save your changes. You have now reset the administrator's password.
Repeat the previous process for any additional administrator accounts.