It is not exactly easy.. but anyway, Look around under the filter holder (that big black thing) and you should see how to do it.
It's been so long since I worked on my old 4af .. hmm I know that there is an emissions line that comes off of the cat and connects to the cover there It's a big hose u gotta disconnect that.. There might be a screw or 2 in the cover.. I can't really say I don't remember

.. just fool around with it and yank on it.. u'll be able to figure out what you gotta do to get it off.. if it feels like it is really really held on there when u pull at it.. there is probably a few screws holding it on.