It's an interference fit on the tapered and keyed shaft, sometimes a quick sharp tap with a hammer sideways on the tube section will break them free. Note I said "quick sharp" don't flog the crap out of it or you may damage the shaft. Squirt some penetrating spray in there as well to help loosen it. The proper way is to install the centre bolt loosely and put a puller on it, if you don't have a puller you could easily make one up if you're a bit handy.
Another way is to hit it on each side of the tube with 2 hammer faces at the same time, need a bit of co-ordination for this one so don't try it after too many beers
If you can't manage to co-ordinate 2 hammers at once, hold one big hammer on one side and hit the opposite side with another hammer.