In this case, prevention is better than cure. It's hard to decrypt the encrypted files in most cases. Security vendors came up with decryption tool to decrypt the ransomware encrypted files. There was a large increase in the number of ransomware and an increase in complexity of the encryption algorithms used by them. Hence, the decryption tools created by the ransomware vendors failed to cope sometimes.

http://www.thewindowsclub.com/list-ransomware-decryptor-tools gives you a list of tools meant to decrypt ransomware encrypted files. These tools may not work in all cases of ransomware encryption.