You can do these steps:
Step 1: go to edit theme from the administration page.
Step 2: Click "assets"
You can find and delete them here.
Don't hesitate to give us question!
SEO Booster Team
Are you try: Ctrl + F => paste files that Pagespeed insight told you.
Does it work?
I try in all files with a little blue circular thing, i did CRT + F + the files that it showed on PageSpeed Insights and i didn't find them....