We do have the private keys Sr!
If you have the private keys, then you should:
1. Download Electrum or another wallet. If it's electrum make sure you get it from the official site:
https://electrum.org ; it would not hurt to also
check the signature to make sure you don't get a fake wallet.
2. Import the private keys:
https://bitcoinelectrum.com/importing-your-private-keys-into-electrum/Then you can send the coins wherever you want (make sure you also pay the correct/required transaction fee).
PS. Make sure the computer is not infected; make sure the wallet is the correct one. 50 BTC is a huge amount of money and would be a shame to get it stolen by some hackers.