Profile picture for user б

Can I refuse or change the date of reservations


I have problem with two reservations in my apartment in June. I Need to be out of the country and I closed the all days of the month but now I saw I have two reservations. I change the dates of the one of them but I need of your help . How the guest will find the new dates and is it problem to change them without ask them . Can you support me ? How is supposed right to do ? 
thank you in advance! 

Best regards,