Help On My Fan

One of my 80 mm fans has stopped and I want to replace it. I can not tell how to get them off. I am attaching a large picture of the whole thing and a small section which has the black connection. One side of the screw (?) has no slot for a screwdriver and the other side does not look like a nut that could be screwed off. I am sure many of you have taken these off before. Tell me does the nut screw off or does it come off some other way?

squeeze the pronged black thing with some pliers, it will pop straight off. then just bend them open again slickly to attack the new fan. It should just pop straight back on.

EDIT: or another similar design ive come across involves you pushing something long and thin into the centre of the black thing, which will cause the "thing" to get smaller and thus allowing the fan to come off.

Thank you very much. I would not have guessed to do either of those.