Originally Posted by
sinoflyer
No. You have to buy a new ticket and have the original one refunded, based on its fare rules.
You're basically correct, but it's often possible to change without physically interacting with a human.
Examples:
1. Ctrip (and some other OTAs) can do everything behind the scenes; e.g. if your ticket costs Y600, and the flight you want costs Y700, they simply charge you for the difference plus the change fee, if any
2. If your ticket permits changes, you can change to other flights on the same airline in the same fare class pretty effortlessly, and upfare if needed
3. Full fare tickets are really easy to negotiate with
In all cases, I strongly recommend making changes over the phone or online (I prefer the phone though) rather than in person.