Firstly, you just need to to login, enter your email address and then click "Continue" Enter the password associated with your account and then click "Continue"
From the dashboard on the left hand side, you'll see the option to edit your profile
From here next click on the 'Update your payment details' button
If you'd like to remove your card details just below is a link that says "Update your payment details" Click on this, which then gives you the option to remove this card and enter new details. Click "Remove this card"
It will still give you the option to update your payment details. So prior to a renewal for example, you could add in your card details and then go back through and repeat this process to remove them again if you wish.