If your item is currently booked out then you are not able to change any of these details. The reason for this is that the person who has made the booking has based that decision on factors including the price, location and the condition of the item so the ability to edit your item is only available if there are no bookings.
What you need to do is hide this item from appearing in any further search results and create a new item with your amended details.
Under your account menu select 'My Items' and select the 'Hide' button.
You can then add a new item from your account menu with the updated description, prices and photographs.