How do I replace the alternated on a 2000

SOURCE: 2000 Volkswagen Passat 4Motion 2001 passat v6

When were the sparkplugs,airfilter changed,is there damp in the coil packs or the seals worn allowing in damp.The maf sensor(mounted in airbox top) may be faulty or the throttle throat may need cleaning.Fuel contamination can play a part, how old is the fuel filter as they should be replaced every 2 years.Check that all vacuum pipes are secure and not cracked as leaks can add to the problem.