1. Press Ctrl+O to open the Open dialog.
2. In the left-hand pane (navigation) find the Templates folder and open it.
3. Select Normal.dotm and open it.
4. Press Ctrl+Shift+S to open the Style pane.
5. Right-click the Normal style and choose Modify.
6. In the Modify Style dialog, choose Format, then Font.
7. In the Font dialog, choose the desired font and font size and click OK.
8. Click OK to save the modified style.
9. Press Ctrl+S to save the template, then close it.

If you can't find the normal template, see How to Open the Normal Template. The steps above were given by Suzanne Barnhill, author of the first article.