@Sanja0, you're already on Request Booking, not Instant Book. In fact, it's not possible for a host to activate the Instant Book function until she/he has had at least one completed booking.
I would suggest that you get rid of the Extra Guests No Charge box, as it's misleading. It could cause guests to think they can in fact bring in extra people after the first six.
You can get rid of it by going to your settings and entering a very high amount (e.g. $250) in the Extra Guests No Charge box. Then click on Save. When the page refreshes, the box will be invisible.