Before resetting Active Directory user password, you need to log on domain controller with administrator rights, then follow these steps:

1. Click Start, click Control Panel, double-click Administrative Tools, and then double-click Active Directory Users and Computers.
2. Navigate to the Users item of your Active Directory domain in the left pane.
3. Right-click the domain user account you want to reset the password for in the right pane, and select Reset Password.
4. Type a new password into the Password and Confirm Password boxes.
5. Click OK. Done!