How to remove the comment box and the footer 'Theme by Puro'?

Hi Hyunjoo

Thanks for reaching out 🙂

Remove the attribution link from Appearance > Theme Settings > Footer Attribution Link (near the bottom).

Comments can be globally disabled from Settings > Discussion. Global settings for comments don’t change the comment settings for individual posts or pages. To turn off comments on a specific post or page, edit it, click Screen Options top right, enable Discussion and then scroll down to the Discussion meta box below the Visual editor where you can disable comments. For more on comments and disabling, please, see: http://purothemes.com/documentation/general-wordpress/disable-comments/.

Let me know how it goes.