I have found this in quora , if anyone has any other method to resize especially old uploaded images ,
add_filter('wp_generate_attachment_metadata','ad_limit_media_file_max_size');
function ad_limit_media_file_max_size($image_data) {
if (!isset($image_data['sizes']['large'])) return $image_data;
$upload_dir = wp_upload_dir();
$uploaded_image_location = $upload_dir['basedir'] . '/' .$image_data['file'];
$current_subdir = substr($image_data['file'],0,strrpos($image_data['file'],"/"));
$large_image_location = $upload_dir['basedir'] . '/'.$current_subdir.'/'.$image_data['sizes']['large']['file'];
unlink($uploaded_image_location);
rename($large_image_location,$uploaded_image_location);
$image_data['width'] = $image_data['sizes']['large']['width'];
$image_data['height'] = $image_data['sizes']['large']['height'];
unset($image_data['sizes']['large']);
return $image_data;
}
Quora link:
https://www.quora.com/Is-it-possible-to-create-a-child-theme-in-WordPress-that-loads-faster-than-its-parent
Good luck
Settings/Media
) and used this wpse answer to keep the folder on the server 'clean and uncluttered'. For us it works like a charm and the client is also satisfied with the results.