Here is what you need to do to cancel your subscription, it's very easy...
Log in by clicking on the Login icon at the top right of the Quant Investing website.
After you have logged in, click the Subscriber Icon that appeared at the top right of the website.
Then click on the Manage subscription menu item.
Step 1 On the new page, click the Subscription left menu item.
Step 2 Then click on your email address to show your subscription details.
On the next page, scroll down to the bottom of the page
Click on the Update Card button at the bottom right of the page.