Disable comment form name, url, email or make them optional

Hello,

I want to have 100% anonymous comments (just the comment content) or maybe state that name, email and url should be optional. I haven’t decided which of these goals is going to be used finally so I would be grateful to know how to achieve both of them.

Also I’d like a recommendation for a WP Captcha solution for the comment form.

How should I proceed? I have followed some tutorials from wp beginner and other sites that provide a way to unset these fields. However these tips seem to work with the default theme but not with Franz Josef.

Thank you!