Click the right mouse button on the desktop, choose View and then choose from the options:
This are medium size Windows 7 desktop icons:
Now, use the smart way to resize desktop icons in Windows 7 using the mouse or scroll in touchpad of laptops:
1. Left Click on any empty area of Windows 7 desktop.
2. Hold the CTRL key.
3. Turning the mouse wheel or scroll in touchpad of laptops to increase or decrease the size of icons to any size you want!
Smallest Windows 7 desktop icons: