You will have to remove the intake, and replace the gaskets (they are reuse able but you should have new ones on hand in case they are damaged.
The spark plugs installed in the engine are designed to last for 100k miles, unless you have a misfire, then there really no reason to replace them.
How to change the spark plugs
To change the spark plugs on a 2005 Cadillac CTS 3.6, first, ensure the engine is cool and disconnect the battery. Remove the engine cover to access the spark plugs, then carefully disconnect the ignition coil connectors and remove the coils. Use a spark plug socket to unscrew the old spark plugs, then install the new ones, tightening them to the manufacturer's specifications. Reassemble by reinstalling the coils and connectors, followed by the engine cover, and reconnect the battery.
It is moderately easy to change the spark plugs on a Liberty, although it is rather tricky because of the gap between the spark plugs.
Sell it !!!
Spark plugs and wires
Changing spark plugs is relatively easy. Disconnect the batter and spark plug cables, and remove the old spark plugs. Next replace the spark plugs with new ones, reconnect the spark plug cables and battery.
Have a look at ; www.carbasics.co.uk
This is for the '05 Frontier, but should be what you're looking for. http://www.clubfrontier.org/forums/f23/how-change-spark-plugs-2005-gen-2-frontier-40507/
Disconnect the battery, remove the spark plug cables and boot, and remove the old spark plugs. Put in the new spark plugs, attach the cables and boots, and connect the battery.
usually every 100000
To change the spark plugs in a 2005 Dodge Stratus, first, ensure the engine is cool and disconnect the negative battery cable. Remove the ignition coil or spark plug wire from each spark plug, then use a spark plug socket and ratchet to unscrew and remove the old plugs. Install the new spark plugs by hand to avoid cross-threading, then tighten them to the manufacturer’s recommended torque. Reconnect the ignition coils or spark plug wires and restore the battery connection.
NGK platinum plugs