Be careful here if I were you. Changed a Flex booking myself online once and their online change system doesn't take into account whether you have a Flex or Saver ticket, nor does it display Flex or Saver for your new fare, so you could accidentally change your Economy flights to Saver without realising. I had Flex, changed online, got Saver after the change without realising (more like without being informed of it), and then had to pay MORE to get the Flex back, on top of the change fees I paid to make the change originally!