To remove the cover from the side where the internal cables are pluged in and the motherboard is located, follow these steps:

Raise the upper cover (not the automated document feed). I mean the cover benath the scanner glas.

Now turn the side to you, where you've already removed the screws from.

The side cover is held by some Hooks, so it can be a bit tricky. Start from the right ro remove the cover. Lift up the darker grey plastic parts slightly.