The simplest way by far is to go to an ATM that will buy your BTC for you. There are not many of these out there and chances are that you do not live near one. If you do and you do use it you will likely receive somewhat of a discount verses the market rate.
The next best option would likely be to use coinbase if you are in the US. Once your identity is identified and bank account confirmed you will be able to sell your BTC instantly and receive money in your bank account in only a few days.
Surprised to hear I will get a discount for using an ATM - I thought they generally charged very high fees?
I don't think there is one anywhere near me, sadly though!
So is there nothing like Coinbase for non-US residents yet?