A full drive erasure would certainly do the trick, but it’s not a good idea for getting rid of just one file or folder. A typical emptying of the recycle bin will only remove its connection to the main directory.
The only reason the data is still there is because the computer hasn’t written new data over those areas yet. Choose between one of nine standards of shredding to ensure that file retrieval is impossible.
File Shredder overwrites those specific data blocks that hold your data. In addition, it also has a feature that lets you shred free space.