Welcome. I guess most people on the forum post about using Avios for flights rather than hotels, so it may well be that your question hadn't been answered. I tried a dummy booking as I guessed the terms and conditions must be there somewhere, and indeed at stage 3/6 ("Price") it had the following under a "Policies" button

Changing your booking: You will not be able to change your booking when it has been confirmed. You will be able to cancel your booking, for a fee, and make a new booking. However, we cannot guarantee that the same hotel room or car rental option will still be available.

Cancelling your booking: Cancellations made outside of 72 hours to travel will not be charged a supplier fee but you will be charged a cancellation fee of £25 or local equivalent. Cancellations made within 72 hours to travel will be charged 100% of the booking value and no refund will be made. Failure to cancel prior to scheduled check-in time will be considered a no-show and will not be eligible for refund. There will be no refund for unused services or early check-out.

Cancellation fees: In addition to the hotel cancellation policy described below, there will be an additional fee equivalent to £15 for any cancellations made by an agent over the phone. Cancellations made online are only subject to applicable supplier cancellation fees.