[Sakin]

I am not so sure what are you talking about. So in category page, you want all the image from left to be at the top of image with full size. Then for this, you need to build child theme. You can check this http://catchthemes.com/blog/create-child-theme-wordpress/ out for child theme.
Then you need to copy content.php from your parent theme to child theme and then replace the code <?php the_post_thumbnail( 'featured' ); ?> with <?php the_post_thumbnail( 'full' ); ?> or <?php the_post_thumbnail( 'large' ); ?>

[Sakin]

@rickm813: It will take the page content before more tag (more…)