I seem to constantly struggle with keeping the numbering in headings straight. I have read various articles on this but this article is the best way of doing this:
https://blogs.msdn.microsoft.com/timid/2013/08/29/stupid-microsoft-word-trick-multilevel-numbered-headings/
https://wordknowhow.wordpress.com/2013/01/30/how-to-use-multilevel-numbered-headings-in-the-word/
Works with Microsoft Office 2016 too!
