So you set your WordPress installation up in a sub-folder on your site. (Something like wordpressblog.com/wordpress/.) And now you want to take your WordPress site to the root URL of your site. (Like wordpressblog.com.) It’s actually a bit simpler than it seems!
The first step is to find where your wp-config.php file is located. Once you’ve found it, find the index.php file in the same directory.
Open index.php and copy the code. It should look something like this:
Now, go to your root folder and make a new index.php.
Paste the contents of what you copied into the new index.php. Now, you see on line 17 where it says /wp-blog-header.php? Before the / place your WordPress folder’s name.
For example, if your WordPress installation lives at wordpressblog.com/wordpress/ your new index.php would look like this:
Save that file. Now, the next step is to go to your WordPress admin and Settings » General.
Change the Site Address (URL) to your root site URL. Save. You should be done and your site should be live at your root URL. Yay!