Exchanges
The fastest way to ensure you get what you want is to return the item you have, and once the return is accepted, make a separate purchase for the new item.
European Union 14 day cooling off period
Notwithstanding the above, if merchandise is being shipped into the European Union, you have the right to cancel or return your order within 14 days for any reason and without justification. As above, your item must be in the same condition that you received it, unworn or unused, with tags, and in its original packaging. You’ll also need the receipt or proof of purchase.