I need help with changing them. Do I have to take off the intake maniford to change the last three. If not, then where are they? Thanks

 

This job is easier than it might appear at first glance.

1) Remove front bank rocker cover ornament.
2) Disconnect six ignition coil harness connectors. Three are found under
the ornament. Three more are found nestled among the plenum runners, in
plain view, closer to the windshield than the three which were hidden under
the ornament.
3) Loosen ignition coil fixing bolts and pull out six coils from the intake
manifold connectors.
4) Use a spark plug socket, a long extension, and a ratchet handle to remove
the spark plugs.
5) I recommend using a tiny dab of anti-seize compound on the threads of the
new spark plugs.
6) Tighten the new plugs to 14 - 22 foot-pounds.

See http://vbxmaxima.8m.com/sparkplug.html

See also Chapter 8, "Do It Yourself", in your Maxima Owner's Manual.