There is no charge if you are upgrading. I have done it almost every trip. If you are booked under a pin code, make sure you ask if there ae any rooms at that pin. If the pin is expired, the rep will have to call (i think it is called) the customer service desk and ask if they have any rooms available with that pin. I changed from a MK tower room at the CR to the BLT 1 bedroom and our pin had expired (meaning I had it, but it was no longer available to the general public). I kept calling and calling only to be told it wasn't available and when I finally thought to say I had booked under an expired pin and maybe she needed to call the CS desk, it was than that she did call them and I was upgraded at no charge. I hope that helps.