If the event you have purchased tickets for is cancelled or postponed, you should notify the seller in order to receive either a refund of the amount you paid for the tickets or replacement tickets for the new event date, depending on the particular instructions issued by the event organisers. 

If a refund is provided by the seller, it is not required to include a refund of any delivery costs, and you will not be entitled to claim any associated costs such as travel, accommodation or loss of earnings etc.