Unable to make changes to <head> #345

Hello, I'm trying to add an adsense script to but I am unable to figure out how. I don't know if this is a good place to ask, but could someone tell me how to archive this? It's a simple <script> header, but the file structure is so different that I can't find it. I figure it's in a, HTML file somewhere, or PHP file, but I can't find the specific location, so any help would be nice.

Also I apologize if this is a bad place to ask, I can't find any links to support server or anything, so This is my only option to ask for the assistance. So, I do apologize.