Default Returning back to stock?

Sending back my month old certified like new replacement with speaker failures.

I need to return to S-on stock before doing so. I just want to clarify what to do before I dive in. Can anyone take a minute to help me?

1. First I need to download something from below...but which one?

2. Then follow steps here

3. Done

Am I missing anything? I dont want to screw this up. I cant afford to get a new phone right now. Thanks in advance, I know this is sorta a noobish thing to do but the search bar is missing from my screen at the moment in all forums so I didnt have a chance to do all of the searching I planned to do.
There is no substitute for reading about the software you are about to alter your $700 device with.