You can enter your address manually if you have a new build property.  To do this, go to checkout and when entering the billing address, click on the relevant link as below 

If your house is difficult for the courier to find, please add short courier notes in the box.

If you have registered for a web account and wish to change your address on your account you can do so by logging in and use the ' account information' tab and then the ' update' button. 

To change an address on an order, please contact us as soon as possible. If we can catch your order before it moves to picking and packing, we will amend it for you. Please call rather than wait for a reply to an email as we may not get to your order in time. You can find our phone number here. 

If this does not fully answer your query, and you are not able to find a relevant article, please raise a Support ticket using this link