Reset all file permissions - is it possible?

We have a ReadyNAS NV+. One of the users has been logged in on the admin account for two years, therefore all of the files he has created are not editable by other users.

I found the link below and was contemplating running this on the drive to reset all the permissions, but wanted to get a 2nd option before I break potentially it!

http://lallousx86.wordpress.com/2009/06/14/resetting-ntfs-files-security-and-permission-in-windows-7/

We have about 120 GB of files, the only way I have been able to reset the permissions is to go individually file by file, I tried at the drive level as well as at the folder level many times with no changes. Also, with the computer programs we use, it is not an option to move of copy all of the files elsewhere as the files reference each other in AutoCAD via file path locations. Any help would be greatly appreciated!