It's a small trick that's clever. Actually they give you the tip just before the Asylum Demon.
The thing is, when you come out of the tower onto the parapet, turn around and look next to the door. Hidden slightly in shadow, you'll see a ladder.
Apart from clearing the crossbow undead from the top, try leading the Taurus demon to the base of the tower, quickly climb the ladder and then - what can you do from the top?
Well, the answer is...*need some spoiler tags on blogger!*
Jump off and press R1/light attack, to do the dive attack the tutorial before the Asylum demon taught you.
You can actually do this multiple times - dive attack, run away, dodge his attack then run past him back to the ladder. Freak out that you're not going to climb it fast enough as you climb it, get to the top and stab him in the head again! And again!
And now you know!