Open up the wp-config.php file of WordPress. Add this line to it: Change the URL accordingly, so if you want your installation in shred-fat.info/wordpress add /wordpress to it.
PHP:
define('WP_SITEURL', 'http://www.shred-fat.info');
This will make it so the WordPress installation directory would be your domain root.
Then, move all your WordPress files into your desired folder.
The error message is saying that wp-blog-header.php doesn't exist. Did you accidentally delete that file?
Also, how much content do you already have on your blog/site? If you don't have much, it would be easier simply to delete the entire folder and start over. You seem to have two WordPress installations. Simply delete the entire folder with the installation you wanted to change. Then upload the WordPress files into your new folder and reinstall it again.