How to reset a user's password in Active Directory
Active Directory allows Windows network administrators to centrally manage the user accounts, and other resources on a network. Users can use a single username and password to log in to any computer on the Active Directory domain. If you forget your password, you can reset it from the Active Directory Users management console. You must be an Active Directory administrator with the proper permissions to reset a user's password.
Click "Start," type "Mmc" into the search box at the bottom of the Start menu and press "Enter." If you don't see the search box, click "Run," type "Mmc" into the run dialog and press "Enter."
Click the "File" menu in the MMC window, and select "Add/Remove Snap-in."
Click "Add" to view the list of available snap-ins, select "Active Directory Users and Computers" in the list and click "Add."
Click the "Close" button, then click the "OK" button.
Navigate to the "Active Directory Users and Computers/Domain/Users" snap-in in the left pane, where "Domain" is the name of your Active Directory domain.
Right-click the name of the user you want to reset the password for in the right pane, and select "Reset Password."
Type a new password into the Password and Confirm Password boxes.