Securely Delete Files
You can securely delete files by going to the Finder menu and selecting down to “Secure Empty Trash”.
Secure Delete actually writes zeros over the data rather than just freeing up the space on the disk, thus increasing security by making the file nearly inaccessible, at least by any simple data recovery methods.
This is particularly useful for removing any sensitive data or files you don’t want anyone else to dig up, like when you’re transferring your Mac to a new owner. Note that deleting files in this secure manner takes longer than the typical file deletion method. If you do plan on changing the ownership of a Mac, you should ideally go a step further and securely format the entire drive, but that’s a topic for another post.

[...] secure empty, which is also accessible via the Finder menu, will take a bit longer than emptying the Trash as normal, this is because the [...]