To cancel your monthly membership head to the My Membership section under My Account, and click 'View Details' beside the membership you wish to cancel.
On your membership detail page you will see the option to Cancel Membership.
You'll land on a final confirmation screen which will display when your membership will remain valid until (dependant on the terms set up by the business).
Note. If you agreed to a contract period, your membership will not end until the minimum term has been reached.