Can't change "Blog – Die aktuellsten Neuigkeiten"

Hello,
in this forum I found several hints to change this title to the post title, but I can’t change this. In the official link http://kriesi.at/documentation/enfold/replace-the-default-blog-latest-news-title/ there is a code, but no clear info in which file I have to insert this. I think this is the function.php, but this don’t work.

<?php
/*
* Add your own functions here. You can also copy some of the theme functions into this file. 
* WordPress will use those functions instead of the original functions then.
*/
?>
<?php
add_filter('avf_title_args', 'fix_single_post_title', 10, 2);
function fix_single_post_title($args,$id)
{
    if ( $args['title'] == 'Blog - Die aktuellsten Neuigkeiten' )
    {
        $args['title'] = get_the_title($id);
        $args['link'] = get_permalink($id);
        $args['heading'] = 'h1';
    }

    return $args;
}
?>

Do I have misunderstand something?