The cancellation charges depend on the hotel, time of stay ('season' time, 'off-season' time), and time of cancellation. To know what's applicable in your case, check the hotel's policy mentioned on the booking page while making the reservation (in case you missed it, This information is also included in your confirmation email. In case you have availed any discount on your bookings through promo codes, the cancellation charge is applied on the undiscounted price.
You can usually cancel or change your booking up to 24 hours before your planned arrival time.
Please note that if your room is non-refundable or part of a special deal, it may have a different policy.