Changing a font & style in Windows 7 is simple if you follow the steps given below.
1. Right-click on Desktop and select Personalize.
2. Click on Window Color.
3. On Windows Color page, click Advanced appearance and settings to see Window Color and Appearance.
4. Here you can change the font and font style (bold or italic). To change the text font, select Icon from the Item drop down list and then change the Font to your desired one from the default Segoe UI.
You can also change the size of texts under Windows Color and Appearance.
5. Click Apply button to save the changes.