YOu would have to call member services and have them shorten your original reservation by 4 days. This would free up points. Then you can use those points to book somewhere else. You would run the risk that in the time it took to do the modification with Member Services, the resort you wanted to switch to could be taken. For this reason, I would do the whole thing with Member Services. Tell them what you are trying to accomplish. They could tell if the resort you wanted the 4 days at was almost sold out or if there was plenty of availability. They could then do both transactions.