NiceHash does not provide exchange services as we are a mining platform only.
You will receive the reward (if you mined a block) to your external address in the cryptocurrency of the package you were mining. Make sure that you always provide the correct address. For example if you were mining with a Gold S Package (Bitcoin) then you will receive BTC. Once the funds are in your wallet, you can transfer them to any of your preferred exchanges and change to another currency.