- Uninstall everything you no longer require
- Remove all folders you nolonger require
- Delete all documents phots etc. from the my documents folder
- Use CCleaner to clear all temp files
- Use CCleaner to clean the registry
- Use Cleaner (Tools Drive wiper) to Wipe free space (you can set the number of passes 7 will be good enough so that nothing can be recovered) but it will take along while to complete its probably an overnight job.
What is ransomware and how do I protect my PC from Petya?