Upgrade Advice

Processor: Intel core i5 4670K
Motherboard: Z87 Msi MPOWER.
RAM: 8GB PNY at 1600Mhz
Hard Drive: 125gb Kingston SSD and 2tb Seagate HDD.
Video Card: Nvidia GTX 760 EVGA 2GB.
Power Supply: 75O watts, FSP Group.

Hello.

What should I upgrade If I want to run smoothly future games like The Division, The Witcher 3 or Battlefield Hardline?
Currently my FPS in Battlefield 4 is from 60 to 80, (except in firestorm)

I'm thinking on buying another GTX 760 and use it in SLI mode with the one I have, talking about the processor I was thinking on a 17 4770K, but it seems it wouldn't improve much; unfortunately I can only upgrade one component.
So, what do you guys think?

Performance will come from the gpu and the cpu

i would say the gpu,i5(i see 3.8 speed on turbo) is fine,i even doubt you will need more than 2 cores

Wait until those games come out and then see if you need to upgrade. If you wait then parts will be cheaper if you need to upgrade.

First I would recommend upgrading your PSU to a Corsair RM750 or CX750M if you can. I'm not sure about FSP but I haven't ever heard someone recommend these, but safe power delivery is very important to the lifetime of your hardware, and with such a nice everything else I would try to do that.
Next thing would be the GPU. Dual 760's would kick some serious ass. Just know that not all games are going to work right with SLI. You shouldn't have to many issues, since the second card will default to a dedicated PhysX processor.
After those two items I would get more RAM. 8GB is great, but once you have 16GB of RAM you just can't go back.
Finally BF4 was designed well for multi-core CPUs, so a 4770k would give you a performance increase but not by much.

p.s. Check out Corsair's ForceLX SSD's. Storing all your games on an SSD will help load times tremendously and the SanDisk ReadyCahce 32GB SSD for cahce. Its a beautiful combo

The i5 is fine for now as long as you're just gaming. If you do any kind of recording of your games like streaming etc then I'd consider upgrading to an i7. Other than that there is no reason to upgrade the processor if all you do is gaming. Hell half the games now barley use 2 cores and almost non use Hyper-threading... The GPU is okay for now, but I'd consider upgrading the GPU to a 780 or get a 2nd 760 and run a 2 way SLI setup. And NEVER EVER cheap out on a PSU. Stick with known brands like Corsair or Seasonic. I can't count how many times I have seen a rig fail because of a cheap PSU delivering unstable power.