You should ring the airlines concerned and cancel those flights. After cancelling you may want to call back and have them check that your remaining flights are still showing.

We had a few problems with LanChile not registering our cancellation phonecall. We showed up at the airport and were told "their system" showed that we had no flights. We explained that we had called them previously and cancelled some flights and they reinstated our bookings. Then on our next lot of flights we were told that as we hadn't cancelled our flights (the original cancelled ones) that all our flights had been cancelled. After explaining the whole saga again thay were reinstated.