My advice
pay someone else to do it !
seriously tho I changed mine very easily with the engine out but with engine in place i cannot imagine how hard it would be !
they are located at the back above the exhaust manifold and you will be very lucky to see them let alone get any tools in there.
i have heard of some people who have managed to change them but dont know how but apparently you need double jointed arms,wrists etc and a big box of plasters
sorry to have to tell you this
good luck