Although the previous version of the Dragon capsule was flightworthy enough to deliver supplies, its life support system wasn't reliable for human passengers. Dragon V2, on the other hand, will be able to carry seven astronauts for seven days.
When the capsule reaches the ISS, it will dock with the station autonomously. Unlike its predecessor, it won't need the ISS's robotic arm to reach out and grab it.
And this isn't the only improvement. To land back on Earth, version one slowed its speed with parachutes before splashing into the ocean. For the new capsule, this is a backup technique. Because the V2 can use its engines to land propulsively.