You will be liable for the costs of returning any unwanted goods unless the trader has specifically agreed to cover the costs of returns. Information about this can be found in the terms and conditions.
However, you cannot be held liable for the costs of returning goods if the trader failed to inform you of that fact before you placed your order or has not told you how much it will cost to return the goods, if they cannot be returned by normal post.
If you decide to cancel your order, you must return the goods within 14 days of your notice of cancellation. It is worth keeping the receipt from the post office in case you later need to prove that you returned the goods within the deadline.