Hi Dinara,
Try to add this code inside functions.php
function remove_comment_fields($fields) {
unset($fields['email']);
unset($fields['url']);
return $fields;
}
add_filter('comment_form_default_fields', 'remove_comment_fields');
This may solve your problem.
We recommended not to change the code because if you change the code then while updating to our new version
all your customization code will be lost. So better make child theme and first unhook the functions and the
edit the code.
http://codex.wordpress.org/Child_Themes
Thank you!