Booking an additional night is only possible when the offer allows it and it is of course, subject to availability.
I.e. If the offer you booked was for 2, 3 or 4 nights and you booked 3 nights, you can contact our travel advisors to check whether there is availability to extend your holiday to a fourth night. However if the offer you booked is, for example, for 7 or 14 nights and you booked 7, it is unfortunately not possible to extend the length of your stay for one night. Please remember that for any change you need to contact our travel advisors who will assist you when the changes are possible, or inform you when they are not.