I bought a second hand Blackberry recently, and although it had been wiped, it still had the previous IT policy on there.
To remove it, I found a 32bit PC and downloaded JL_Cmder from here.
You will also need the BlackBerry desktop software which you can get here.
Then simply plug in your BlackBerry via the mini USB cable and run JL_Cmder. You can then select option 5, Reset to Factory.