I had booked a 21-day advance rate, which is non-cancellable.

I then noticed that the new 21-day advance rate is lower. I called the toll-free hilton.com number and the agent said that he could not revise my rate to the lower one. However, he transferred me directly to the hotel and told me to ask for the front desk.

The hotel front desk politely cancelled my original reservation and told me that I could now re-book the new lower rate online.

Thanks, Hilton, for the nice, friendly service!