Editing # of rooms

[Shan16]

Hello!

Trying to figure out how to edit the number of rooms my home can support. I currently have it listed showing that renters can rent the whole house but want to adjust it to reflect that I only want to rent 2 bedrooms without cancelling any of the reservations that have already booked the whole house. 

Is there a way to say that - "after this date guests can only book two bedrooms"? Or do I have to wait for the guests that have booked the whole house to complete their trip before I can edit this? 

Thanks