To remove that nut, first lightly score across the slot in the fretboard on both sides of the nut with a scalpel or razor blade.
This is just to break any seam of glue that may be there from the factory.
The nut should be able to be driven out sideways with a small hammer and a drift, rather than trying to prise it out from the end or from the top (prising it out like that is a good way to damage the fretboard). To do this, you need something to use as a drift, so preferably something flat on the end and close to the thickness of the nut (I don't recommend a screwdriver or anything chisel-like).
A couple of light taps with the drift up against the end of the nut is all it should take to get it to move. If the factory has gone stupid with the glue (doesn't look like in the photo in post #15) it may take a bit more persuasion, but you don't want to bash it to the point of damaging the fretboard (or the nut if you can help it). That said, I have seen nuts that ultimately had to be destroyed in order to remove them, but this should be a big minority of cases.
If it's really stuck, come back here for more advice before breaking out the sledge hammer and vise-grips!