Yes no one donated it but I want to get private keys since I could want to switch to another wallet.
Actually, it's quite easy. Go to Wallet -> Private keys and select Export. This will show different private key for each of your addresses.
If you want to export your Master Private Key from which it is possible to generate all of your addresses then you have to do a few more things.
Go to View and select Show Console
All you have to do is to input "getmasterprivate()" and then you will be able to copy your Master Private Key.
Do you have the 12 words which you were given while you were creating your wallet? They can be also used for wallet recovery and this might be actually more convenient than the process described above.