The right to change your mind
Thanks to 'cooling-off periods', you can cancel your order for any reason within at least 7 days from receiving the order (more in some countries) and send it back.
The seller must give you a refund within 30 days. You may have to pay the cost of sending goods back to the seller, though.
[!] Some purchases are not covered by the cooling-off periods, for example hotel bookings, car rental and travel tickets.