It should be in the footer.php file

It goes in your templates footer.php file right before the closing body tag </body>

First, go to your admin panel, on the left side click 'Appearance'
Next, click 'Editor' and look to the right. You'll see THEME FILES. Scroll to the link that says 'Footer' click on it to open up the HTML codes.
Once you open up the Footer panel, scroll down till you see something that look like this:<?php wp_footer(); ?>
<!-- #footer -->
</div>
</div>
<?php if(get_option('ds_footer_tracker')) echo stripslashes(get_option('ds_footer_tracker')); ?>
</body>
</html>

Then put your mouse on "<" before the "body". Click your mouse, then hit "enter" key to space the place for your Google codes. Right click your mouse and a dialogue box will open for you to paste your code. That's it! close every thing and you are done.

If you find this too difficult check this FREE report from Craig Desorcy. He is a fine man and is equally handy to help you. Check him out here at the Forum. Once you get download, go to pages 32-34 for a detailed guidance and screenshots to go help along the way. Any problem, contact warriors here at the forum and someone will do it for you.
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Why don't you use one of the free plugins? No need to edit code. Just add your GA id.