Simply remove the cover from the case of the computer, disconnect the cables from the drive and then unmount the drive - it is usually held in by some screws, normally with Philips heads,. size 0 or 1.
Having done that,. a great use for such a drive is to put it in an external drive enclosure to use it as a backup or external storage drive. Even better is if you use a network cable caddy and you put it on your network so all the machines can access it.
If all you want to do is to blank the drive and you don't really want the drive then I suggest going to dban.org and downloading their software. That will blank your drive so thoroughly that not even the NSA could get anything off of it.