Because we are 3 old ladies, we don't keep up with too much in the techie industry. Therefore, we are stymied as to how to remove our offensive Legacy Popups and change over to their "new" style of newsletter signups. We can sort of see how to do it, but don't want to mess up the pages, as we have no idea where to put all that code. Any advice?

Hi, mailchimp setup only requires you to insert your API keys you get from Mailchimp.
No code to insert to get that working.
Have you checked out this page? https://www.ecommercetemplates.com/help/mailchimp.asp

Thanks,
David