Traduciendo paso 7
First of, remove the 2 white pieces or rubber on the sides and the middle, grey piece too. The first picture shows you what this will look like.
Then simply "pop" the buttons out (marked out in orange in picture 2) from the other side (the front). You can also remove the "Play Station" logo button.
For the other side, remove the top plastic and then the 4 buttons (made of one piece of plastic).