Wanting to know how difficult it is to change spark plugs on a 1999 chevy lumina six cylinder car?

The rear bank of plugs is not entirely easy to get to and will most likely need to be done by feeling around. Not a problem for people that are familiar with cars. It might be better for you if you find someone that already has an idea of what they are doing and who has the proper tools to do this. Ask around, everyone knows someone that can do maintenance work on cars.

This is actually a pretty easy job if you have the right tool. GM made this engine so it will rotate forward. You disconnect the engine to radiator support strut. Then you install a rotating tool in its place. Put the vehicle in neutral, set the parking brake, chock the wheels. Then turn the screw on the tool and the engine rotates toward the front of the car. The plugs and wires are completely exposed. Without the tool, it's a horrible job.

Try rocking the car back-and-forth. When you have good forward momentum, quickly put on the parking brake. This may create additional room between the engine and the firewall, givng you the ability to change the rear plugs yourself.