How to replace the spark plugs?

There is no pattern to changing them. Just change the all is all that matters. Here are some guides that will help with this:

https://www.2carpros.com/articles/how-to-tune-up-a-car-engine

https://www.youtube.com/watch?v=e68QXyBAiZo

Here is the process from the manual that shows how to replace them. Please run through all this material and let us know if you have questions. Thanks