Welcome to FlyerTalk.

Did you read the detailed fare rules before purchasing? It's often useful to actually print those to a PDF orbthe like forvtimes like these. Or, purchase a more expensive refundable fare.

For changes such as you want on a discount fare, it's typical for an airline to 1) charge a change fee, and 2) recalculate the fare - including increases that might be in effect now because the cheaper fares have been taken up (or if they're advance purchase fares the advance purchase period has expired).

It's true - when you fail to show up for a sector, all further sectors will automatically be canceled.

If there was a significant schedule change (e.g. 2 hours or more, or one making you lose a connection) imposed on you by changing airline schedules, you'd be able to cancel and refund the entire fare, but failing that I think you're stuck with the few choices pointed out previously.