I'm about to do this to my cases, so no pics yet. The instructions are in German, if memory serves, but fortunately, I speak German, so it's not too hard.
The instructions say remove the rivets fixing the "screw" locks, so that you can remove them from the catches.
Then stick the template stickers on the catches, and use a file of some kind to match the shape shown on the sticker.
I'll be buying an ordinary metal file, and attempting to do it by hand, I think.
Once the integral locks fit the new cutout, fit them inside, and use the little metal clip to hold it in place.
Of course, whether it's as easy as the instructions say is another matter.