Changing flights is a complex process that involves a lot of rules (differences in applicable fare classes, collecting additional fees or possibly issuing partial refunds, etc). Like any complex business process, it would cost a lot of money to develop an easy-to-use/intuitive web-based interface for it that any user (not a professionally trained ticketing agent) could use. The investment to build such a web application is simply not worth it for most airlines and travel sites. They make their money from ticket sales, not from ticket changes, so it's logical that this is where they would invest. Very few people will specifically prefer to buy from travel provider X only because travel provider X has an easy web-based way of changing tickets. And ticket change fees are usually high enough to more than justify the hourly rate of the ticketing agent manually changing the ticket over the phone. Having said all this, if you are a savvy traveler, you can speed up the manual process by doing your research ahead of time (find the exact flight you want to change to online, find out if it has the fare class you need, etc) - this way, it's a simple matter of telling the flight number and date to the phone agent.