The easiest way to replace the rear plugs is to remove the upper and l;ower cowling assemblies. Don't forget to plug your wiper motor nack in when re-assembling (Been there...Done that
1. Remove both wiper arms.
2. remove upper (outer cowl)
3. Unbolt lower cowl
4. Unplug wiper assembly
5. Unhook washer hose.
There's your rear plugs.
If you have 75,000+ miles and not done before, may I suggest also replacing the coil pack. These have been known to cause slight mis-fires after this mileage and will keep you from having to remove the cowls again to replace. That will be your call though.
I would also recommend while you're at it, a new set of OEM wires and dielectrical grease on the boot ends to eliminate any spark leakage.
I prefer iridium plugs as they take less energy to fire and is a lot less demanding on the ignition system.
I also use Permatex copper anti-sieze on spark plugs. The aluminum ant-sieze tends to set up from the high temp enviroment.