Via 'Your Account'
Once logged in, access ‘My Account’ via the top right
Go to the ‘My Addresses’ page, here you can either update an existing address or add a new one.
When submitting an order, once you reach ’03. Address’ you will see the option to ‘Add a new address’, or Update the existing Delivery and Billing addresses.
To add a message to your order, once you reach '03. Address' of the checkout process there will be a box where you can add any additional comments.