where would i put this php code in my wordpress post template?

echo str_replace(',', ' ',

<?php get_header(); ?>
<?php if (get_option('flex_feat_display') == "no" OR get_option('flex_feat_pages') == "home only") { ?>
<?php } else { ?>
<?php if (get_option('flex_header_trans') == "yes" && get_option('flex_feat_trans') == "yes" && get_option('flex_nav_position') == "below") { ?>
	<script type="text/javascript">
	jQuery("#nav").css("border-bottom","solid <?php echo get_option('flex_blog_borderwidth'); ?>px #<?php echo get_option('flex_blog_bordercolor'); ?>");
	</script>
<?php } ?>
<div id="feature">
	<div class="topshadow">
		<?php if ( function_exists('dynamic_sidebar') && dynamic_sidebar('Top Feature') ) : else : ?>
		<?php include (TEMPLATEPATH . '/feature.php'); ?>
		<?php endif; ?>
		<div style="clear:both;"></div>
	</div>
</div>
<?php } ?>
<?php if (get_option('flex_nav_show') == "yes" && (get_option('flex_nav_position') == "below feature")) {
include (TEMPLATEPATH . '/includes/nav.inc.php');
} ?>
<div id="content">
	 <?php if (get_option('flex_adsense_loc1') == "yes" && !get_option('flex_adsense_loc1banner')) { ?>
  <div style="width:730px;height:90px;display:block;margin:5px auto 15px auto;text-align:center;">
    <?php 

	$adsize = get_option('flex_adsense_loc1size');

	$adtype = get_option('flex_adsense_loc1type');
	
	$adchannel = get_option('flex_adsense_loc1channel');

	include('adsense.php'); ?>
  </div>
  <?php } else if (get_option('flex_adsense_loc1') == "yes" && get_option('flex_adsense_loc1banner')) { ?>
   <div style="width:730px;height:90px;display:block;margin:5px auto 15px auto;text-align:center;">
   <?php echo stripslashes(get_option('flex_adsense_loc1banner'));  ?>
   </div>
   <?php } ?>
   <?php if (get_option('flex_lsb_show') == "yes" && get_option('flex_lsb_pos') == "left of post") { get_sidebar('left'); } ?>
	<div class="postwrap">
		<?php if (have_posts()) : ?>
		<?php while (have_posts()) : the_post(); ?>
		<div class="post" id="post-<?php the_ID(); ?>">
			<div class="posthead">
				<h1><?php the_title(); ?></h1>
				<?php if (get_option('flex_metadata_show') == "yes") { ?>
				<div class="postMeta">
					<div class="postdate">
						<?php the_time('l, F jS, Y') ?>
						at
						<?php the_time() ?>
						 
						<?php edit_post_link('Edit'); ?>
					</div>
					<div style="clear:both;"></div>
				</div>
				<?php } ?>
			</div>
			<div class="postcontent">
				<?php if (get_option('flex_adsense_loc4') == "yes" && !get_option('flex_adsense_loc4banner')) { ?>
				<div style="display:block; margin:10px 0 15px 0;">
					<?php 
					$adsize = get_option('flex_adsense_loc4size');
					$adtype = get_option('flex_adsense_loc4type');	
					$adchannel = get_option('flex_adsense_loc*****nel');
					include('adsense.php'); ?>
				</div>
				<?php } else if (get_option('flex_adsense_loc4') == "yes" && get_option('flex_adsense_loc4banner')) { ?>
   <div style="display:block; margin:10px 0 15px 0; text-align:center;">
   <?php echo stripslashes(get_option('flex_adsense_loc4banner'));  ?>
   </div>
   <?php } ?>
				<?php the_content('Read the rest of this entry'); ?>
				<?php wp_link_pages('before=<div id="page-links"><p style="text-align:right"><strong>Pages:</strong>&after=</p></div>'); ?>
				<?php if (get_option('flex_show_tags') == "yes") { ?>
				<p><?php the_tags('<strong>Tagged with:</strong> ',' • ',''); ?></p>
				<?php } else { ?>
				<?php } ?>
				<?php if (get_option('flex_show_cats') == "yes") { ?>
				<p><strong>Filed under: </strong><?php the_category(' • '); ?></p>
				<?php } else { ?>
				<?php } ?>
				<?php if (get_option('flex_show_like') == "yes") { ?>
				<p><strong>Like this post?</strong> <a href="<?php if (get_option('flex_email_address')) { echo get_option('flex_email_address'); } else { bloginfo_rss('rss2_url');} ?>">Subscribe to my RSS feed</a> and get loads more! </p>
				<?php } ?>
                
                <?php if (get_option('flex_adsense_loc5') == "yes" && !get_option('flex_adsense_loc5banner')) { ?>
				<div style="display:block; margin:10px 0 15px 0;">
					<?php 
					$adsize = get_option('flex_adsense_loc5size');
					$adtype = get_option('flex_adsense_loc5type');	
					$adchannel = get_option('flex_adsense_loc5channel');
					include('adsense.php'); ?>
				</div>
				<?php } else if (get_option('flex_adsense_loc5') == "yes" && get_option('flex_adsense_loc5banner')) { ?>
   <div style="display:block; margin:10px 0 15px 0; text-align:center;">
   <?php echo stripslashes(get_option('flex_adsense_loc5banner'));  ?>
   </div>
   <?php } ?>
		</div>
		<div class="clearer"></div>
			</div>
			
		<?php if (get_option('flex_metadata_comoff') == "yes") { ?>
		<ul class="Note">
			<?php if ( comments_open() ) : ?>
			<li class="NoteRss">
				<?php post_comments_feed_link( $link_text = 'Comments RSS Feed') ?>
			</li>
			<?php endif; ?>
			<?php if ( pings_open() ) : ?>
			<li class="NoteTrackBack"><a href="<?php trackback_url() ?>" rel="trackback">
				<?php _e('TrackBack <abbr title="Uniform Resource Identifier">URI</abbr>'); ?>
				</a></li>
			<?php endif; ?>
		</ul>
		<?php comments_template('', true); ?>
		<?php } ?>
		<?php endwhile; else : ?>
		<h2>
			<?php _e('Not Found'); ?>
		</h2>
		<p>
			<?php _e('Sorry, but the page you requested cannot be found.'); ?>
		</p>
		<?php endif; ?>
	</div>
    <?php if (get_option('flex_lsb_show') == "yes" && get_option('flex_lsb_pos') == "right of post") { get_sidebar('left'); } ?>
	<?php if (get_option('flex_rsb_show') == "yes" || !get_option('flex_rsb_show')) { get_sidebar(); } ?>
</div>
<?php get_footer(); ?>

<?php
if ( !function_exists('byeByeCommas')) {
    function byeByeCommas($content){
        $content = str_replace (",", " ", $content);
        return $content;
    }
}
?>

<?php the_content('Read the rest of this entry'); ?>

<?php echo byeByeCommas(the_content()); ?>

add_filter ('the_content', 'getRidOfCommas');

function getRidOfCommas($content) {
   if(is_single()) {
      $content = str_replace (",", " ", $content);
   }
   return $content;
}

<?php
if ( !function_exists('byeByeCommas')) {
    function byeByeCommas($content){
        $content = str_replace (",", """, $content);
        return $content;
    }
}
?>

str_replace (",", '"', $content);