Honestly, Personally I don’t recommend to add Google Analytics.
I don’t know why you cann’t edit header.php file. I’ve to take a look(i forgot your web address).
YOAST Plugin has default options to add Analytics Code.
Simply you can use Plugins also: https://wordpress.org/plugins/google-analytics-for-wordpress/
I was not able to find the header.php file, where do I click to navigate there? Normally there is an option for “editor” in the theme that shows all of the files and you can add from there. But, in the Elevation theme, I don’t see that option. The theme editor just allows you to edit appearance of pages and such.
The last theme I used actually had a section in the them to add the analytics right into the theme. I prefer to not use a lot of plugins, lot’s of bad reviews or slow down of sites on the one you mentioned.