This other forum covers both changing the plugs and another component of the engine, scroll down about two-thirds for some useful input on the back set of plugs that are more difficult to change than the front three.
http://www.myfordfreestyle.com/forums/viewtopic.php?f=1&t=2537
( 6 ) spark plugs
To change the spark plugs on a 2005 Ford Freestyle, first, ensure the engine is cool and disconnect the negative battery terminal. Remove the ignition coil by unscrewing the bolts and gently pulling it off the spark plug. Use a spark plug socket to carefully unscrew the old spark plugs, then install the new plugs by hand to avoid cross-threading, and tighten them to the manufacturer's specified torque. Finally, reattach the ignition coils and reconnect the battery terminal.
How to change the spark plugs
There are six plugs. The plugs are located at the end of the spark plug wire. There are 2 banks of plugs. One bank you can see and the other bank is located ib the back of the engine.
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.
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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.
According to the 2005 Ford Freestyle Owner Guide : For the 3.0 litre Duratec V6 engine the spark plugs are gapped at ( .052 to .056 inch ) * confirm with the Vehicle Emissions Control Information ( VECI ) decal in the front of your engine compartment