As long as an order has not been paid, you may still cancel it. Simply click at the top on:
Orders --> Customer Orders
In every unpaid / open order you have an option to cancel. Please contact support if you need to remove the cancellation from an order.
Once orders have been transferred to the lab for production, there is a very limited possibility to still cancel it. Please contact our support staff immediately so that we may ask the lab if the order in question has been produced already or if it can still be cancelled. This also depends on the amount of products ordered and the product types.