Provide the theme summaries for the following conversation: 

#Person1#: Good morning. Ru Via Hotel, Room Reservation. Can I help you?
#Person2#: Yes. This is Peter calling from New York, I have to change the date of reservation.
#Person1#: How and in whose name has the reservation been made?
#Person2#: By telephone and in my name.
#Person1#: Please wait a moment. I'll check it in the computer. Thanks for your waiting. You've booked 10 standard rooms for trade negotiation for March 5th, 6th and 7th, is it correct?
#Person2#: Right, but the negotiation has been postponed until 5th to 7th of April. Do you think it's possible for us to change the reservation?
#Person1#: Let me check the reservation list. Fortunately, we have just 10 standard rooms available for the three days.

Summary: 
Peter calls Ru Via Hotel to postpone the date of the room reservation, and #Person1# tells him there are rooms available.