How to disable multisite
Running multiple sites like this may not be for everyone. You may have decided to switch back. It’s pretty easy, so here’s how.
Delete any extra sites you may have created. Move the content and users to the main blog or wherever you desire.
Remove the lines we added in the wp-config.php file.
Restore the .htaccess file to the default. One the multisite lines are gone from the config file, you can usually restore these by resaving the permalinks.
Drop these global tables in the database:
This is an excerpt from the free ebook Create a Network in WordPress.