Right click on your (Windows) Desktop and select Properties.
Click on the Appearance tab
Click on the Advanced button to get the "Advanced Appearance" Dialog
There is a message on the dialog that says that settings will be overridden
if you are not using Windows Classic View - although this is true for
colours, it is not true for Scrollbar size so you can ignore it.
Under Item, click on the dropdown arrow and select Scrollbar from the list.
Change the size to however big you want it - the preview picture in the
dialog gives you an idea how big it's getting.
Click on OK on the Advanced Appearance dialog
Click on OK on the Display Properties dialog
It takes a moment or two, and you're done
