2004 Chevy Cavalier spark plugs

Engine Performance problem
2004 Chevy Cavalier 4 cyl Front Wheel Drive Automatic 65.000 miles

I went to a autozone to ask where the plugs are located and they told me under a sheild on the top of the engine, done that and engine Died, so can you please tell me where excactly are the located and how easy is it to do. To many things in the way compared to older vehicles where it is so easy to do also this is the first time I want to change them had the car for almost four years. Use to get a quarter tank going up north now it is using a half a tank. Thats why I feel they need changed.
thank you