Hope this helps: here https://support.apple.com/en-us/HT202255 you’ll find how the built-in version history works (versioning system shown up first time in OS X Lion) and then delete all unwanted/useless versions. BTW, If you’re hurry (or just snorty) just type a simple “sudo rm -rf /.DocumentRevisions-V100” in Terminal to clean up all the (mis)used space. Please, note that after this command should be better rebuild the Finder index…