HOW OFTEN DOES BITCOIN MINING DIFFICULTY CHANGES IN A MONTH????

I am pretty new to the cryptocurrency world but i have done thorough research and have bought coins that were and/or are below $1 like Dogecoin,Siacoin,ripple,Mooncoin and Golem. But recently i developed an interest to start mining Bitcoin and Altcoins on Genesis Mining, I personally think it's a profitable contract to venture in and i am planning to buy an open ended BTC 20 TH/s which will cost me $2600 and i will have ROI roughly in 6 months.What got me thinking is that when i was doing my research about cloud mining reviews(mostly in Forums, that's where you find genuine reviews) i came across bad and good reviews and seemingly the bad reviews outweighed the good ones and that the good ones were accompanied by DISCOUNT CODES.

  1. How often does the BITCOIN mining difficulty changes in a month?
  2. Is upgrading the contracts frequently the solution to countermining.jpgMining Difficulty and get your ROI as indicated upon purchase?
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Difficulty retarget every 2016 with a mean block time of 10 minutes..
But specific block time is fluctuating a lot!

@wessell is it ok to buy these cloud mining contracts get the ROI

Unless the price of BTC drops a lot, you should be able to make money on cloud mining. But it's still risky and there is no guarantee you will make your investment back.