Originally Posted by
Often1
+1 - What OP wants is to change the reservation. That means repricing at current levels. Do do otherwise would encourage people to book the cheap rate for the maximum possible length which may be needed and to preserve the rate later.
... which is why you book multiple one-night stays - assuming they are all priced the same - when you aren't fully sure of your plans.
Fifth night free wouldn't even apply to the OP's premium room booking.