Renumbering subheadings on TOC on MS-Word 2007?

Word 2007 continues the subheading numbering when I create a TOC; e.g., Heading I has three subheadings A,B,C, so Heading II begins with D rather than starting a new A. How do I get it to restart the numbering?

Also the TOC will not reflect all the levels that I’ve created. How to fix?