Turn on file sharing for Private Networks. You can setup shares on each system with just the directory you want to share. Share with only the accounts you want to share with. For example, I use the same Windows email account to log into all four of my Windows systems. Since the password is the same for all, you can setup sharing for that one person only. You can also setup sharing for Everyone, but it's a little less secure. To share a directory, right-click on it and select 'Share with'. The dialogue box will come up so you can choose who to share with.
You can do the same or use different accounts, but you have to enter the credentials for that user on that system. Once you do that and select remember credentials, it will allow you to browse, edit or delete files on the other system (depending on the rights you setup).