Hi, I want to remove 'Email' and 'URL' fields from the item comment block . I dont think the email is necessary for my site since only registered users can post comments. Thanks

You can override the output of the templates as already suggested here:
www.joomlaworks.net/forum/k2-en/44225-reposition-comments-after-media but you have to keep the email field. You can hide with CSS though.