@Bobby: Since it's Word 2007 it would be Office button > Word Options > Proofing section > Autocorrect options button > AutoFormat / AutoFormat as you type.
But straight quotes / smart quotes does not change the first quote to be a lower typographic quote necessarily. It depends on the language set for the paragraph (or whole document).
For example, in French you get left and right "angle" quotes, in English you get curly left and right quotes (66 and 99).
German will get the lower / upper quote you describe.
So, you can turn off smart quotes to affect things going forward, but then everything you do is straight quotes only. It won't fix the problem of quotes that are already in your document. Better to set the language of the paragraph to what you want and the style of quotes will follow the tradition for that region.
Select paragraphs you want to change (or Ctrl-A for all). Review ribbon > Language > Set proofing language > choose a language > OK.
Edit: turns out that switching the language won't fix existing ones either. Best bet will be to switch the language first, then use find / replace to correct ones you already have.