You can only make changes to your booking by going directly to the Cineplex where you booked your tickets. This is subject to seat availability for the movie and/or showtime that you want to change to.
You need to make the changes at the box office at least 2 hours before the movie showtime that you originally booked.
No changes can be made after the movie that you originally booked has started. All tickets and bookings fees are non-refundable.