If you open up the properties dialog for the top level folder you want to set permissions on then open up the Security tab, you will find a button there for advanced settings. Open that dialog up and in there there will be a check box saying something like "reset permissions on all child objects and enable propagation of inheritable permissions". Check that box and hit the "apply" button. This will reset permissions on all files and subfolders of this folder. I have attached a screenshot which may help.
Government is like fire - a handy servant, but a dangerous master - George Washington
Government is not reason, it is not eloquence - it is force. - George Washington.