Having purchased the ticket from Expedia, you might have an extra level of complexity in getting the ticket changed. It does not hurt to call, though.
Whatever you do, don't just be a no-show because it's almost certain to wreck your return. Even on airlines where they don't require a round trip purchase for a particular fare, a missed flight usually cancels the entire rest of the itinerary. They figure if you didn't do A to B, you're not going to do B to A.