Yes it is possible to unlock the cores on your particular CPU, but it's not guaranteed, nor is it very helpful to have 6 cores rather than 4 cores when gaming at this point in time. You will most likely not reach 4.0 GHz with that cooler, but you'll probably get 3.7 or 3.8 GHz. Ocing might give you an extra, say, 3-10 fps in CPU intensive games, although most games are GPU limited rather than CPU. Anyway, here is the most basic procedure for getting a decent OC with your CPU...
1. Clean out your case. Make sure your cables are neatly managed. You're going to need it with the relatively basic CPU cooler that you have.
2. Install Prime95 and HWMonitor (for temps).
3. Go into your BIOS and increase the CPU multiplier to 17.0 (3.4GHz), leave the Vcore (CPU voltage) and RAM timings alone for now.
4. Run Prime 95 (select "small FFT" test) for 15 minutes or so to determine CPU stability and max CPU core temps.
4a). Keep in mind that the maximum CPU core temps should be no higher than 58C or so.
5. If all is well and system seems stable, increase the multiplier to by 0.5 (3.5 GHz).
6. Repeat steps 3 and 4 until system is unstable or CPU temps rise to 58C.
7. Once you have what you believe is your highest OC settings, run a "blend" test or small FFTs again in Prime95 for a few hours to ensure you actually have a stable machine. This isn't necessary, but it's good procedure.
Messing with the Vcore, FSB, and RAM is a little weird and unnecessary for new AMD black edition OCers unless you absolutely have to have that last 200 MHz or so when using a basic cooler, but if that is the case with you, there are plenty of articles and guides on Tom's that will show you how. Good luck!