At the top of the screen, click the down arrow next to your avatar and name, then select 'My Account' from the drop down list.
Then select the 'Subscription' tab.
You will be shown the details of your current plan. Clicking 'Downgrade to Free Account' button will then cancel your "Premium" subscription. You will still have access to our awesome services until the end of your billing cycle. You will receive an email shortly after this action has been completed confirming your last day of "Premium" access.