Just because they are recoverable does not mean you need to securely erase to clear up space on your drive.
Download OmniDiskSweeper. It will help you find large files to delete and clear up space.
I need to clear space on my computer. How do you really erase files? I know with the trash can they are still recoverable.
Until trash is emptied, that space is still taken on your HDD. Once you empty trash, then that space is available to be overwrriten as necessary. It is then essentially 'free' space.