If you image’s return value is on “Image Object”, you can grab the full size easily. Look at the code below:
<?php while(has_sub_field('top_links')): ?>
<li>
<a href="<?php the_sub_field( 'link_url'); ?>" target="_blank">
<img src="<?php $image = get_sub_field('link_image'); echo $image['url'] ?>">
</a>
</li>
<?php endwhile ?>
