To change the size of your desktop icons in Windows 7, right-click on a blank area on the desktop, hover your mouse over View, and select one of the three provided sizes for the desktop icons. The provided sizes include small, medium and large.
In Windows Vista, click Classic Icons on the View shortcut menu to select the smallest size for the desktop icons. Alternatively, click on a blank area on the desktop, press and hold the Control key on your keyboard, and scroll the mouse wheel up and down to change the size of the desktop icons. Release the Control key after selecting the desired size.