*Using the Windows interface
Open Active Directory Users and Computers.
In the console tree, click Users.
Or, click the folder that contains the user account.
In the details pane, right-click the user whose password you want to reset, and then click Reset Password.
Type and confirm the password.
If you want to require the user to change this password at the next logon process, select the User must change password at next logon check box.
To perform this procedure, you must be a member of the Account Operators group, Domain Admins group, or the Enterprise Admins group in Active Directory, or you must have been delegated the appropriate authority. As a security best practice, consider using Run as to perform this procedure. For more information, see Default local groups, Default groups, and Using Run as.
To open Active Directory Users and Computers, click Start, click Control Panel, double-click Administrative Tools, and then double-click Active Directory Users and Computers.
Services that are authenticated with a user account must be reset if the password for the service's user account is changed.
*Using a command line