For low-cost carrier tickets these are most often non-changeable and non-refundable. All additional requests including seating, luggage and special equipment (e.g. sport equipment) need to be made at the point of booking and may carry a charge. You may be able to add additional services after booking but you will need to pay the airline directly (if permitted).
We strongly recommend using the online check-in facility offered by your carrier to avoid unexpected costs at the airport.
Please contact your local Travel Expert for more information.