For the SEO experts:
A long time ago, I created a website with some pages that used underscores instead of hyphens to separate words (e.g., "page_1.html"). I understand now that Google likes hyphens a lot better than underscores, so I want to change those pages (e.g., "page-1.html"). These pages already rank very well on Google, but I want to make sure they are ranking as well as possible, hence I want to make this change. (And I assume the redirects won't hurt the SEO they already have)
I know how to set up 301 directs with htaccess file, so that's not the issue. My question: once I get the 301 redirects in place, do I submit the OLD page URL to Google Search Console for re-indexing or the NEW page URL?
Also, should I delete the old page files once the redirects are in place, or keep them, or it doesn't matter?