If you installed your blog on a separate folder example yourdomain.com/blog/index.php and you want to move it to become yourdomain.com/index.php. Go and to your control panel and select the domain forwarding to redirect to yourdomain.com/blog/index.php.

OR

If you've not yet installed or can delete and start afresh, while installing the blog (example WORDPRESS OR JOOMLA) from FANTASTICO (if CPanel) make sure you follow the steps comprehensively to a stage it will ask where you want to install, just include a slash(/) example yourdomain.com/ it will install into the root folder of your host.

This should work!!