How To Show Full Size Image Wordpress Attachment Page in 3 Steps

Step 1 : If your theme don't have attachment.php page copy single.php and paste it in same theme folder

Step 2: Locate and delete <?php the_content(); ?>

Step 3 : Add this code

<a href="<?php echo $post->guid; ?>"><img src="<?php echo $post->guid; ?>" alt="<?php the_title(); ?>"  /></a>

Now your attachment page will display full size image with a link to oriinal file.