Does it have risk? Of course! every investment has its risk, it doesn't matter whether you invest your money on Bitcoin or other currencies, there's still risk. It can't be 100% safe.
Every investment involves certain level of risk, as we are not aware how it will perform in future or how long it will survive and same thing goes with bitcoin too, Invest that you can afford to loose.
But it hard to know when you have to sell it and that is the hard thing of it.
I dont' think there is anything hard in it, if you see higher price then the purchase you made then you should sell it without waiting to long and buy it again when price falls.