You can decrease the size of your icons by heading to the link at the bottom of the resolution screen called 'Make text and other items larger or smaller'.
This will bring you to a window with three options;
'Smaller - 100%' which as it says is the default; this is the setting that you'll want.
The other two are for larger screens; for example on my 32" I use the medium setting of 125%, otherwise my icons require a pair of binoculars to see!