Hi Tom,
I just added roof rails to my 2016 LRDS HSE. Those covers have tabs on the short ends that "spring" into holes in the rail. You'll need the smallest imaginable flat screwdriver or similar flat device (dull razor blade?) to try to compress the tab on either end and gently wedge/pry the end up. From there, you'll see how they're made and how they fit in their hole. Mine were plastic and rather delicate. If you're intending to reuse, reinstall, or sell the rails, you'll want to go slow, cautious and surgical. I would imagine those covers could break easily. When you get the first one, the other covers all behave the same way. Once the cover is removed, all you need is a 13mm socket and rachet to remove the bolts that hold the rail to studs. The studs are built into the body. If you don't put the rails back on, you'll see that there are cavities that you'll probably want to cover.
Good Hunting,
Rob