adjust the code for previous/next post

Hey. I'm building out a theme and putting in the code for previous/next post (which isn't naturally part of the theme and had to be put into a particular folder on SFTP)

This is what they gave me:


// =============================================================================
// -----------------------------------------------------------------------------
// Standard <footer> output for various posts.
// =============================================================================

<?php x_entry_navigation(); ?>
<?php if ( has_tag() ) : ?>
<footer class="entry-footer cf">
<?php echo get_the_tag_list(); ?>
<?php endif; ?>

Which produces this effect:

I'd like those arrows to appear in the center</center> of the page.

Also, they are appearing on the Archive posts -->

And I only want them on the basic posts.

And finally; would You please show me the code to have the featured image appear on the outside (left of the left arrow, right of the right arrow) of the arrows?

Thank you so much!