[Plugin: WP Page Numbers] not understanding wp-page-number instructions

I installed the plugin, but I cannot seeem to get it to work.

The instructions say:
Replace the the ‘next_posts_link()’ and ‘previous_posts_link()’ with the code below in your theme (archive.php, index.php or search.php).

<?php if(function_exists('wp_page_numbers')) { wp_page_numbers(); } ?>

Starting with my index.php, the only relevant code I find is:

<?php
$prev_link = get_previous_posts_link(__('Newer Entries »', 'kubrick'));
$next_link = get_next_posts_link(__('« Older Entries', 'kubrick'));
?>
<?php if ($prev_link || $next_link): ?>
<div class="art-Post">
    <div class="art-Post-body">
<div class="art-Post-inner art-article">

<div class="art-PostContent">

<div class="navigation">
	<div class="alignleft"><?php echo $next_link; ?></div>
	<div class="alignright"><?php echo $prev_link; ?></div>

Any help on what I need to change would be greatly appreciated.