You can change the font in any part of Windows (for example, menus). Changing a Windows font doesn't change your program
fonts. You have to change the font in all other applications.
If you are referring to desktop themes, then I would suggest you to refer to the suggestion given by Ronnie Vernon on
18th February, 2010 and CatMParker on 21st May, 2010 in the following thread and check.