Removing google analytics from twenty fourteen

I would like to use analytics as a plug in rather than within a theme so that if I change themes I don’t lose analytics. I have this code in my site when I view the source code.
<script async="" src="//www.google-analytics.com/analytics.js"></script>
I believe this is for google analytics and might have been installed as an option when originally setting up the theme? Not sure how to remove this code (if this is that code?) so I don’t have the script in there twice? I can see the code using a browser but how do I get at it in WP? Please be very specific!

Also installed wpbeginner’s “install headers and footers” plugin and used that to put the analytics snippet into every page (and post?) of my site? I’m guessing since this is a plugin it will keep my analytics if I switch themes?
I am using twenty fourteen with a child theme at https://www.ashevilleontap.com
Thanks for any help in advance and please explain what you say in detail you won’t hurt my feelings.