It's not easy, such profit is usually made with high-risk operations, like trading/holding altcoins.
Best way to tranform 2 btc into 4 is to put everything on primedice xD
You'll have nearly 50%chance to win what you want!
it is the fastest way, and not the best way, because it has a high risk. I think the best way is do trade atlcoin, it was better than any way in my opinion. because I myself have experience about it.