You will unlock the Hall of Darkness when you use your 7th star/blood stone. This allows you to pay 1,000 gold to reset all your stat, ability, and talent points, among other options as well.
This is halfway through the total amount of stones you need to use, as the final room is unlocked at 13 stones.
Be careful with your respec though, and always save before hand. You will lose all skills you currently know, and will have to repurchase the books. It's suggested to try to buy all the books before the respec. This can be a problem, as several skill books will no longer be sold by any merchants as you level up. I only know of Whirlwind and Barrage from my own playthrough, but there are others.
One last thing to keep in mind with respecs is if you took the Lone Wolf trait. You will gain back all your ability points from selecting it, even if you do not reselect it. The downside though, is that respecing won't give you a party slot back, but re selecting the trait will lower your slots again by one. This is most likely a bug, but one that has not been fixed yet (As of August 20 at least).
29 Dec 2015 Edit:
I'm not 100% sure about differences in respecing between the original and the enhanced edition. While it will work similarly, and is unlocked at the same time, the details may or may not be any different.