OK, so here is where it got tricky for me. You'll notice that the back doesn't come off very easily. You'll need to get a spudger or something to (gently!) pry at the gap between the cover and the body. Don't try to pry it all the way off - just lift it off a bit.

The reason it doesn't come off easily is because underneath the cover, on the top and bottom edge, are plastic clips that lock into slots in the body. See the photos to show what they look like. Unfortunately the photo of the bottom only shows 2 of the 3 clips.

As far as I can tell, you need to insert something underneath once you've pried it up a bit to pull the plastic hooks toward the outside edge to have them release. I didn't realize this when I tried removing the cover, and as a result broke the plastic clips.

Even if I did know of them, not sure how I would have been able to pull them to allow them to release - the gap is quite narrow.

I don't think breaking the clips is the end of the world. They help secure the top and bottom edge, but I was able to reassemble anyway, though I imagine in the future there's a greater risk of a gap appearing at the top and bottom edges.