you have to yank it off, but I'm not sure exactly how, some people pull the base off while trying to get just the aerial off :S

so hold the base tightly on! :)
 
a lad i know had the same problem. on my 05plate cupra, i just gave it a good hard pull and it came on but when i tried on his 07plate ibiza it didn't want to come off
 
i just unscrewed the old one, then just pulled. feels like your guna pull the roof off lol but it comes off pretty easy
 

That's the one I have. Was only 6 pounds about a month ago.
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don't try to bend your aerial to kind of lever it out. I did that and snapped the screw. Had to get it out with pliers.
 
I think it depends more on where you live and what the reception is like there

I have had stubby aerials on all previous cars and had virtually no reception, but then I barely get radio with the standard one! If you're lucky and live in an area with good reception I'm sure you'd see no difference!