single.php içeriğiniz templates/single-post/content bu klasörde ama bir deneyin bu şekilde.
Öncelikle image.php ve attachment.php adında 2 dosya oluşturun ve içeriğini alttaki kodlar ile doldurun. Daha sonra tema klasörünüzün içine yükleyin. Ve resimlerinize tıklayın.

<?php
 
defined( 'ABSPATH' ) || exit; // Exit if accessed directly
 
get_header(); ?>
 
    <div <?php tie_content_column_attr(); ?>>
 
 
<?php next_image_link($size, '<div class="alignleft" style="
    margin-bottom: 10px;
    margin-left: 10px;
    width: 110px;
    height: 25px;
    background-color: #86761f;
    border-radius: 4px;
    line-height: 25px;
font-size: 14px;
    border: 1px solid #7d743f;"><font color="#fff">  « Önceki Resim</font></div>' ); ?>




<?php previous_image_link($size, '<div class="alignright"style="
    margin-bottom: 10px;
    margin-right: 10px;
    width: 110px;
    height: 25px;
    background-color: #86761f;
    border-radius: 4px;
    line-height: 25px;
font-size: 14px;
    border: 1px solid #7d743f;
"><font color="#fff"> Sonraki Resim »</font></div>' ); ?></br>

<?php endif;?>


</br><center><div class="entry-attachment">
<?php
// code copied from adjacent_image_link() in wp-include/media.php
$attachments = array_values(get_children( array('post_parent' => $post->post_parent, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => 'ASC', 'orderby' => 'menu_order ID') ));
foreach ( $attachments as $k => $attachment )
  if ( $attachment->ID == $post->ID )
    break;

$next_url =  isset($attachments[$k+1]) ? get_permalink($attachments[$k+1]->ID) : get_permalink($attachments[0]->ID);
?>

<div class="attachment"><a href="<?php echo $next_url; ?>" title="<?php the_title(); ?>"><?php echo wp_get_attachment_image( $post->ID, 'large' );  ?></a></div>

</div>


</br>


<p>Konuya Geri Dön: <a href="<?php echo get_permalink($post->post_parent); ?>"><?php echo get_the_title($post->post_parent); ?></a></p></center>

    <?php endif; ?>
 
<?php get_footer(); ?>