As always, the update would be coming to them over-the-air. It would also probably take a few days for the update to make it to all devices, as is customary as such rollouts are usually staggered.
Should you own an unlocked or a Dev version of the One (M8), then make sure to check for updates as you might be in for a pleasant surprise. After applying the Lollipop update, you would be running build 4.16.1540.8. The download takes 500 MB of memory.