I am about to change the plugs on my '05 Corolla, 99,600km, and have a couple of questions.

Sorry if this has been covered, I tried searching, but with no luck, mostly because I am having a hard time to describe my first issue. Ok, I was about to pull the plugs to have a look at their condition. I tried to remove the plastic cover which covers the spark plugs/wires and valve cover. I removed two bolts just in front of center line of the engine, but there is still two more plastic plugs in the back. what/why and how do you remove these. seams if toyota thought this dust cover rig needed to be secured in four location, they could have used four bolts. or are they just trying to make it difficult?