Note: The photos are for a Fabia combi MK2 (545), but this description should also apply to the Fabia mk2 hatchback, Skoda Roomster, Superb combi (3TS), Yeti (5L), Seat Exeo combi (3R5), VW Tiguan (5N), VW Touran and a few others from those years (~2007..~2015)

First remove the plastic cap that covers the centre axis:
It has 2 small tabs (see figure below). You can push them out a bit with a flat screwdriver from inside the sprinkler aperture and they will come loose.

Then you pivot the cap 90 degrees towards the arm and it comes out without any force.

 

Undo the nut (13mm) that holds the arm.

 

Now, if you are lucky, wiggling the arm (with some strength) it will come loose of the shaft.
Unfortunately the original metal ring in the arm is aluminium which can easily rust into the shaft.
(you may try an anti-rust spray)
If that does not work, the recommendation from VW is to remove the spray nozzle and use an extractor tool to pull the arm from the shaft.
In my case, even that was not enough (a lot of road salt is used here). So after removing the plastic part of the arm (which was broken anyhow) I cut thru the aluminium ring with a small metal blade. As the aluminium ring, is quite soft, it took just a couple of minutes with practically no force applied. Then with a pair of pliers it was possible to remove the remainder of the ring.
If you do this, beware that the shaft has a conical shape where the arm sits.

 

Before installing the new arm you may want to apply some copper grease to prevent rusting of the new one.
Also, run the rear wiper so it sits in the resting position before placing the new arm.
Be sure to place the new arm horizontally, and give it a try before tightening fully.
The tightening torque for the nut is 12Nm .

 

This video shows things quite nicely too:
https://www.youtube.com/watch?v=bsDNLDWnkYM

Maybe add in that you should clean up the exposed thread and (tapered)spline hub before applying some grease, which might be better to use than copper grease - then fitting the (new in your case) wiper arm on.

 

Quite a lot of salt used in parts of UK too, did you check that the spray nozzle remains pointing vertically upwards while the wiper moves from side to side?

 

I managed to remove the wiper arm on my wife's old Polo, but, I was only removing it to fit a repair kit to the wiper motor, so crushing the end of the wiper shaft/spray bar with the puller did not bother me.

... Or use a nut splitter, if you are afraid to sw through the nut. They are usually only a few quid for a pair that can be used on many sizes, over and over so are a handy addition to the toolkit! You just slide the relevant splitter over the nut and tighten bit by bit with a spanner or ratchet, until its built in blade cracks the nut open. 

Hi - anyone got any advice?

I unfortunately snapped off the top part of the threaded metal with the bolt nut. (12 years of rust)

I then had to saw off the metal from the wiper arm which was no problem.

Now I have a bolt with most of the thread stuck inside.

I can buy a new bolt nut (I assume it's just a 13" from a hardware store) but I doubt I've enough metal left to turn it onto (maybe 2 rings - it could be enough).

Anyone got any ideas?

Am considering trying to glue the wiper arm to the bolt with epoxy resin though not sure how well/long that would hold.

Apart from that the only alternative I can think of is switching the entire wiper motor which is gonna be expensive and time consuming.

Thanks!