It's easy, I do that often.
Change your JOOMLA configuration.php in the root:
FIND:
public $log_path = '/home/somename/domains/domain.nl/public_html/yoursubdomain/logs';
public $tmp_path = '/home/somename/domains/domain.nl/public_html/yoursubdomain/tmp';
- Remove /yoursubdomain and move the whole site to root.
- Than login as admin and check your SETTINGS > GLOBAL CONFIGURATION
- Empty caches.
- If you edit your .htaccess file (I assume you did not, check it for redirects.
That's all. 2 Minutes work
To be sure, backup first.