Using a small screwdriver (i.e. the Torx T6) just push the plastic bar and it should slide out the other side.

Now the cover should just come loose. It also separates all of the exterior components so you can take the back off without it pivoting around the bar!

Be careful of the two plastic pieces in the sides of the case. They aren't really attached to anything and are basically just spacers. Keep them safe on your parts tray.