Originally Posted by SRQ Guy

I have done this three times.

Call Priceline. Ignore the many prompts that will tell you "no refunds or changes any time". Persist until you speak to a live operator. In my experience they will grant you a "one-time" exception, where they will allow you to cancel the reservation (minus the Priceline fee). The way it works is that they will send you a cancellation form. You have to then bid again for the same number of nights in the same zone at the same star rating for the new, correct dates. If you are successful and have your bid accepted, you will then enter your new reservation # into the cancellation form, email it back, and they'll cancel the old reservation. Be persistent, they should let you do it.

Alternatively, call the hotel directly and explain your predicament. I had a Hampton Inn here in the USA change the date of a stay for me for no charge when I screwed up a Priceline reservation once.