Please download and extract the zip file so that you have an xml file.
Login to the admin side of your store and go to "Manage Hooks" and click on the "Import Code Snippets" tab. Select the xml file on your computer and click import.
After import you can change the quantity level by clicking on "Disable checkout until minumum order quantity is met" in the code snippet tab. In the text field you will see the PHP code. The value for $min_order_quantity can be changed to the level you want.