I've replaced dozens over the years on my tdis, they are easy provided they were not overtorqued the last time they were changed. Your socket needs to be a quality 6pt deep well. Not sure on torque spec. You can use a basic $10 multimeter to test the plugs individually for resistance ohms. If your car is an ALH (03 should be) I have plugs in stock in my garage if you want to shoot up to Noblesville sometime. send me a PM.
if you want to buy them and do it yourself, do yourself a favor and order from (aaron) bleachedbora. boraparts.com good price, high quality, quick ship, etc. Be aware that cyls 3 and 4 doesn't always mean those are the bad plugs, in my experience. Test them individually or get a set and replace them all. It will save you time, aggravation, and wear and tear on your bridge harness. IMHO it is not worth doing one at a time, unless you like looking at your CEL. OK, rant is over.