Managing your subscripiton couldn't be easier. Just go to your account on the following link:
Log in with your account details
And you will see a history of all previous orders, which you can click and expand to see more information.
The button on the right hand side called "MANAGE SUBSCRIPTION" will take you through to this page where you can update your payment details, shipping address, skip or amend deliveries and amend the products in you subscription.