Some users may wish to increase the default Windows Vista font size, perhaps to help overcome visual impairments. Thankfully, the Microsoft team have made it really easy to perform this task and have added some other accessibility options which you can read about.
To increase the font size, right click anywhere on the empty part of the desktop and then click Personalize:
Now, click Adjust Font Size (DPI) on the left hand menu:
Then you can choose the font size you wish to use. If you want to increase the font, select Larger Scale (120dpi) and then click OK:
If you would rather specify your own custom font size, click the Custom DPI button and then enter your own values. You will need to restart the PC for any font size changes to take effect.