XF 2.1 How do I locate the <head> and </head> tags to insert code for AdSense?


I'm not sure if I'm posting this in the right forum, so mods and admins please feel free to relocate this question to the most appropriate place on the site.

I'm still pretty new to running a website and doing my best to learn. I want to use Google's AdSense to generate a little bit of revenue (I hope). I don't know where to find the site's <head> and </head> tags to insert the code for AdSense. Can anyone help me understand where to find this?