Absolutely normal, where You have learned such a method? You cannot never delete files or folder which are in use, which are read only, if You don't have permission, etc.
Open google.com and search for "Wipe Drive", "Wipe Partition", "Kill Partition" etc.
But I'm not sure, that You should wipe or kill something. Usually is enough if You format this drive or partition. I recomend to use deep format, but if You don't know, how to do, even Quick Format helps.
And then re-install os and programs. If it is done, You can use CCleaner or Glary Utilities and wipe free space, if You have HDD drive. If You have SSD drive, even this is not needed, simply run Trim Drive.