In your dashboard, go to Billing > Pricing Plan.
At the bottom of the page (you have to scroll down) you'll find a big banner saying:
"Want to cancel your subscription?"
Just click on "Cancel Subscription Plan" and your subscription will be canceled.
You will be able to keep using the paid tools until the end of the subscription period, but there won't be any further renewals.
If you have any questions, please send us an email to firstname.lastname@example.org and we're happy to help.