I'm not exactly sure where the plugs are on that engine, but I wouldn't mess with them even if I did. They've been in there for 11 years through lots of heat cycles and are probably rusted in. You could easily strip them or break them. I would remove the upper and lower radiator hoses from the engine and put a water hose in the holes and flush it out that way. I would start with the lower and then switch to the upper. You will probably need to pull the thermostat (this is a good time to replace the thermostat with a fresh one (cheap insurance)) to make it flush better. You will still have pure water in the block, but just compenstate for this when you fill the radiator with coolant to get close to a mix of 50/50 coolant to water.