Changing to Flex Fare is not considered an upgrade from Saver Fare, since upgrade means a different class of service. So from Y to J for example is an upgrade, while Flex or Saver doesn't mean a different class of service (you have saver business class tickets). Therefore you will need to look at your ticket restrictions and "change" your flight to the same flight at a higher booking class which means paying the change penalty. You'll have to pass through EK service line or your travel agent to do it.