Follow these steps.
First, create a child theme of the default theme if you haven't done so already. Under Design -> Themes
this will create a new child theme folder with theme_config.php and screenshot.png files.
Next, copy the partials/header.php from the parent theme to the child theme maintaining the folder structure.. ex tastyigniter-orange-theme/partials/header.php ==> tastyigniter-orange-theme-child/partials/header.php
Within the header.php file under your new theme folder..
Replace the following code with your GA Tracking script....
<?php echo get_theme_options('ga_tracking_code'); ?>
with
// your GA script
<script>
...
</script>
Thats it..
