The best way to increase your bitcoins is by investing them in different altcoins and with that you will be making regular profits at regular time and it will also help you in multiplying your bitcoins which will eventually increase the level of your coins in your wallet.
This, but to add to this statement I will suggest going for ICO's that's how you get the best price for altcoins.
Yes investing in ico can bring huge profits for you but you need to make sure that you are investing in right projects as many icos have turned out to be scam in the past where only the devs have made money out of it living their investors penniless.
Research is the only thing that an investor can do to make sure that he is investing to the right projects because if he didn't do research then he is very vulnerable for the scam projects that are available everywhere because the price of bitcoin is now high so the scams are very common now. If you have patience then read and watch the possible source of information for an ICO so you will not regret if you will invest.