If it's your own site, or the owner has asked you to update the site, then the hosting service should be able to provide the ftp password.

If it's someone else's site, what you're asking how to do is illegal and unethical.

Can you please clarify the situation, so that you don't wind up, even inadvertently, asking for tips on how to break the law and violate the privacy and property rights of other people?

Chris