What your pointing at is a cap, there is an adjusting nut below the cap.
I highly recommend you get yourself a Gregory's service and repair manual,
It is a great resource to have while working on your car.
There are a few on ebay to choose from
http://www.ebay.com.au/sch/i.html?_nkw=gregorys+corolla&_sacat=0&_odkw=gregorys+corolla&_osacat=0&_trksid=p3286.c0.m270.l1313