Setting Default

What version of Windows?

Right-click on the Desktop
Choose: Properties>Appearance
Under: 'Item', choose 'Icon' and change the font or font size.

I'm assuming you are talking about the Office Suite and not Windows - the operating system.

The default font is set for each Office program.

In Word, go to the Format menu | Font | Font tab; choose the Font, Font Style, and Size you want foryour default. Click the Default button in the lower left corner. Confirm that you wish to change the default font.

In Excel, go to the Tools men | Options | General tab; choose the Font and size you wish for your Standard Font.

In Powerpoint:
1. Open an existing presentation or create a new one.
2. Change the presentation (Fonts, font size and style, format) to suit your needs.
3. On the File menu, click Save As.
4. In the Save as type box, click Design Template.
5. In the File name box, type Blank Presentation, and then click Save.
6. If a message box is displayed, click Yes to replace the existing blank presentation.

Hope this helps.