Start by disconnecting the cable from the negative terminal of the battery in order to remove the exhaust manifold. Next, jack up the vehicle and make sure it is securely supported on jackstands. Take off engine splash shields and separate front as well as rear oxygen sensor connectors. Remove heat shields from non-turbocharged models' exhaust pipes and manifold, then remove both cylinder head nuts from exhaust manifold and bolts from exhaust manifold joint on straight six side. On turbocharged models, take off heat shields, then separate right side joint pipe fasteners between turbocharger and manifolds, as well as nuts that attach both cylinder heads to exhaust manifolds. Lastly get rid of the exhaust manifold itself. To install new ones, clean the mating surfaces of each cylinder head, manifold or manifolds and exhaust pipe(s), making sure they are flat without any damages. Put new gaskets on; put a manifold onto cylinder heads; and then tighten down bolts evenly. Afterward attach center pipe or turbocharger joint pipe to this manifold while tightening up all nuts equally connected thereunder. Finally reinstall everything following reverse steps involved in taking it apart but remember to reconnect battery first before testing for proper ventilation once again when turning engine on.