Asking something like this on such a durable engine that rarely see's failures with these parts, might get us asking why you are looking to do so because we might be able to help diagnose it with you. In case it's not lifters or rods.
The procedure will be basically.
Remove fuel rails and electrical connectors to most things on top of the engine.
Remove upper intake/sc
Remove lower intake
Remove front and rear valve covers (if w body this will include the coil pack bracket)
At this point you will have access to the rockers/rods and lifters.
Rocker bolts are considered by GM to be Torque To Yield and are expected to be replaced when you do the job.
