Here is what you need to do to cancel your subscription, its very easy...
Log in at this page http://www.quant-investing.com/login
If you have forgotten your username click the link Forgot your password? below the Login button
After you have logged in click the new menu item Account which will appear in the top menu
On the next page click the Subscriptions button and cancel your subscription or unsubscribe.
You will receive an email to confirm that your subscription has been successfully cancelled.