I had a friend whose desktop looked like the one above. It took me a while, but I finally found the right key combination which actually controls this function.
The steps are:
- Click on one of the icons to select it.
- Hold down the Ctrl key
- With your mouse use the scroll wheel and it will resize the icons.
While this applies to Windows 7, it may also work on other versions.
It will rearrange your icons when you do this so be prepared to move them back to your preferred location.
Here’s the small version below.