If you are trying to remove the metal wiper blade and the refill as one unit you push down on the tab under the arm as seen in you first photo near the lettering. Forgot to mention rock the metal blade so the divit in the hole is not ingaged at the same time.
If you are trying to remove the refill, there should be squeeze tangs near one end OR a single tab at the end of the metal wiper blade that has to be slightly bent up to slide the refill out.
