Change Spark Plugs

You will also need to remove the intake manifold to gain access to the rear plugs, so you will need to get an intake a.K.A. Upper plenum gasket. Never remove the spark plugs hot, you have aluminum heads with steel spark plugs. Always use anti-seize on the threads of the plugs when reinstalling, I like the copper anti-seize. Buy NGK plugs and go quality, they do not make a different length plug for exact application. It will take a few hours to do the project due to the intake manifold.

https://www.2carpros.com/articles/how-to-change-spark-plugs

REPLACEMENT
1. Remove the ignition coil connector (A).
2. Remove the ignition coil.
3. Using a spark plug socket, remove the spark plug.

CAUTION:Be careful that no contaminates enter through the spark plug
holes.

4. When replacing the spark plug, always use the long reach type spark plug.

Do not use a short reach type.
1. Color Marking (Tip).

Unleaded: Yellow Marking

The length is different from the specification above.

3. Part ID.

Unleaded : ILFR5B11

As far as the idle problem, check for vacuum leaks and check the idle air control valve (IAC). The IAC is responsible for maintaining the engine idle speed.

For the spark plug replacement, check out this page.

https://www.2carpros.com/articles/how-to-change-spark-plugs

Let me know if it helps.