I need to change my reservation.

Meaning

I need to alter my booking.

Examples

• John: I'm calling to change my travel plans.
• Alice: Certainly, sir. What changes do you need to make? <b>I need to change my reservation</b>.
• John: Yes, I need to move my return flight to a later date.
• Alice: Okay, let me check availability. It seems we can do that. <b>I need to change my reservation</b> details for you.