The whole point of a password is that it should be difficult to remove. Removal implies that you have authority to do so. A software password is best removed with the utility that installed it, which implies that you have the authority to do so by 'owning' the software. Similarly for a password-protected disk (FDD or HDD). Even Apple's At Ease, which is just an access barrier, needs a careful process to remove it.
The extension of this is that in the absence of knowledge about which kind of protection you are facing, and no access to the means of removing the password, you can do no more than wipe and reformat the disk. Even this will be difficult or awkward if the protection prevents booting from a startup volume of any kind. The password will then have performed its task of protection of drive or files.
If the apparent problem is no more than that a boot (or a data) volume is locked, and the volume mounts on the desktop, see whether Get Info. (highlight the volume's icon, and then press command-i) shows a ticked [checked] Locked box. That is the simplest and least bothersome obstacle to overcome. If the protection is more rigorous in truly needing a password, you have a larger difficulty.
Being of the cast of mind that I am, I should also seriously doubt the bona fides of a downloadable universal 'password killer'. At the very least, run a virus-checker over it before using such a 'utility'.
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