I copied and pasted what I wrote a couple of months ago after changing
mine out:

I just changed out the plugs on my 99 XLT and here is what I came up
with on how to get out each plug on the passengers side:

Remove the inner fender skirt by popping off fasteners.You don't
really need to remove the tire. Just turn it to the left when getting
out the rear plug then turn it to the right when taking out the
middle
and front plug. It's a lot safer to work with the tire on the truck.
At 100K miles, those plugs are really stuck in there. Spray them with
some liquid wrench or WD-40 and let it sit for a while.
You don't need any swivel ratchets. And plus I used a regular 5/8"
deep socket, not a regular spark plug socket with the boot inside. I
found out that removing that type of socket from the spark plug after
you tighten it is hard to get out because the plugs are hard to get
at
with not much space to remove the socket. You could also remove the
boot from the spark plug socket to eliminate this problem.

Rear plug:  When I tried to remove this plug with just a  5/8" spark
plug wrench and a 3/8" drive ratchet, it did not budge. Then I used a
1/2" breaker bar with a conventional 5/8" deep socket. This will give
you enough leverage and torque to loosen the plug. Plus the way the
breaker bar can swivel also helps. Once you get it loose, you can go
back to the conventional ratchet.

Middle Plug:  You have the transmission dipstick tube in the way. The
best way to get it is to put the ratchet (with or without an small
extension,can't remember) between the exhaust manifold and the
dipstick tube. If you can't get it loose, get out the breaker bar
again. Then go back to the regular ratchet, but be careful. As you
loosen the spark plug, the ratchet will start to hit the A/C
evaporator box, so at a point you will have to remove the ratchet and
loosen the plug by hand, which is a pain because your hand will
pretty
much be scraping on the evaporator box, but don't be discouraged, you
will get it out.

Front plug: Same thing. If it does not come loose with a regular
ratchet, use the breaker bar.