I wrote two version of this depending on how your domain is set up;
If you bought your domain from somewhere other then your host...
Well, you'll need to find something called "doman name servers" (or DNS) for your current site. Then go to your domain, or rather, the place you bought the domain, and find a place to switch your DNS. Then go back to your host, find your config.php file, change your domain listed in there. (you have to do this as well in your phpmyadmin, under settings, but I'm not sure) Then go to your host, find a page for making url redirects, and set one up to redirect
http://www.midnighthowl.hostei.com/ to
http://www.midnighthowl.net.
If you bought your domain through your host;
Go to the page to manage your domain and switch the directory your domain is set to point towards. Then repeat the config.php/database part exactly the same way. :3
Tell me if you need more detailed instructions. :3