You can add the Wedding Credit you've purchased, or a Gift Card, to your own account by redeeming this here.
To redeem your credit/gift card, you must log in, click the your name at the top right of the home page, and select 'redeem a gift card'. Enter your code and submit.
Once you have added the credit or gift card, you will need to refresh the page, and the amount of credit in your account will then appear next to your name & cart at the top right of the website, as below:
Please note that if your credit or gift card has been sent from the US site in USD, you will only be able to redeem this on the US site in USD.
Click here to find out more about using store credit.