How to make 'name' field in comment section optional?

So when commenter leaves the field blank, a word ‘anonymous’ could be entered automatically as a comment author’s name. I would also like to disable ‘url’ field. I am using Blaskan theme.

I know, if one goes to discussion settings, you can uncheck a box which says “Comment author must fill out name and e-mail”. But in my case I do want ’email field’ to be filled while ‘name field’ to be either filled or left blank.

Thanks for your time!