These menus are likely a legacy from Word 97-2003. Such menus were easy to edit in that version and cannot be easily edited in the Ribbon versions. If you have Word 2003, open it in that version and right-click on the toolbar. Pick "customize."

If you do not, consider moving the customization to a QAT or Ribbon modification. These are easier (not easy, just easier) to edit in ribbon versions of Word than are custom legacy menus and toolbars.

Modifying the QAT and Ribbon in Microsoft Word

Other than simple QAT modifications, none of these is a simple beginner project in Word 2007 or later. The Ribbon versions were designed to be difficult to customize at the request of corporate IT departments.