第一句：I want to change a reservation.

　　我想更改预定。

　　A: I want to change a reservation.

　　我想更改预定。

　　B: Is the reservation for yourself or for another party?

　　更改你自己的还是别人的？

　　A: For me, please. And my name is Mary?

　　我自己的，我叫玛丽。

　　第二句：I'd like to extend it for two more nights.

　　我想在延期两个晚上。

　　A: What can I do for you, madam?

　　可以为您效劳吗，女士？

　　B: Yes, my name is Alice, and I made a reservation for two more nights until March 8th.

　　是的，我是爱丽丝，我原先预定了两晚的房间，日期是3月5日。我想再延期两晚到3月8日。

　　A: For four nights from March 5th to March 8th. We will make the correction for you.

　　从3月5日到3月8日共四晚。我们给您更改一下。

　　更改预定的相关表达法还有：

　　I'd like to cancel my booking for a single room.

　　我想取消预定的单人房间。

　　I want to cancel my reservation for two nights in the name of Smith.

　　我想取消以史密斯的名字预定的两晚住宿。