Because you do not list the specific date of the cruise, I would suggest checking with your TA or the cruiseline on this.....In general, you cannot just change names on the entire reservation. Usually at least 1 passenger must remain on the booking to make a name change(s), (and at the cruiselines discretion to allow a name change) otherwise it will be considered a cancellation and cruiseline cancellation penalties(if applicable) will be incurred.