You’re currently unable to change your delivery address once you've placed an order. However, if your item hasn't shipped yet, you may be able to ask the retailer to cancel your purchase. You can then place the order again, to your desired address. To cancel, simply follow the instructions under 'Can I cancel my order?'.
If you have an easyShop account and you'd like to amend your delivery address for future orders, simply log in and head to 'Account settings', then 'Addresses'. From there, you can either click 'Add a new address' or 'Edit', to change your current address. If you've added a separate entry, make sure you select the desired address when you next check out.