Change password function in wordpress

function wp_set_password($password,$user_id)
{
       global $wpdb;
       $newpassword = ltrim( $_POST['newpassword']) ;
       $hash = wp_hash_password( $newPassword ) ;
       $wpdb->update( $wpdb->users, array('user_pass' => $hash , 'user_activation_key' => '') , array('ID' => $user_id )) ;

        wp_cache_delete($user_id,'users');
}