Replacing the plugs is fairly easy. Just remove the plastic engine cover then unbolt and remove the 4 coils. Once removed you need to look down and you will see the plugs that need to be removed with a spark plug socket.
How to change the spark plugs
u take the old ones out and replace them by color
Screwed into the head or heads on a V6.
Sell it !!!
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.
There is a cover on top of the engine. Take that off and the spark plugs are right there.
Spark plugs and wires
It is on the crank case cover. Basically on the top of the motor.
Have a look at ; www.carbasics.co.uk
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.
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.