Reduced sharpness of images

I’m a photographer. Images are much sharper until I load them into my theme at the specified 72dpi x 600px. What I read is to “delete the width and height commands from the image code in the html editor” which may solve it. First off, I’m not sure where to access the html editor. Would that be at GoDaddy, the host, or the CSS on in WordPress on my computer?

THE OTHER thing I saw is no add this code, but again, I’m not sure where to place it:

add_filter( ‘post_thumbnail_html’, ‘remove_width_attribute’, 10 );
add_filter( ‘image_send_to_editor’, ‘remove_width_attribute’, 10 );

function remove_width_attribute( $html ) {
$html = preg_replace( ‘/(width|height)=”\d*”\s/’, “”, $html );
return $html;
}

Here’s my site: http://kentannenbaum.com
I really appreciate appreciate any advice. Thanks. Ken