If you got the Reg in a Guerrilla air case, it should of had a hollow allen key, to unscrew the middle of the reg, from there, everything inside the reg comes out leaving it hollow and very easy to unscrew the whole reg, this hollow Allen key is the best bit about these regs, to change any "o" rings or just to tighten due to leaks, If you haven`t got one ? get it from LIPS.
Pennies but well worth having it, I`m amazed at the amount of guys that don`t know about these keys, but there again, a lot buy second hand with and without the bottles.