I thought I'd suggest to look at the MB UK web site but for some odd reason they don't show the face lift while it has been shown at the German site for quite some time (and I thought face lift should come at the same time to all markets, more or less).
The German site anyway shows the main differences, bumpers and lights mainly and some smaller feature changes.
Mercedes-Benz Deutschland - S-Klasse - S-Klasse Limousine