I have default thumbnail size of 150x150px. But I want to change it to 160x240px.. I went to wp-admin/includes/image.php but I dint find any where to change. Could anyone suggest the right place to do that.
To change this... just go into the backend of word press(wp-admin). Settings>Media - you will see it there. Unless your WP is not updated recently.
You must open the index.php to , becouse you'll have to the post title , the image width="put 150" height="put 150". If everything is ok, know you must open this files: category.php , search.php and a few more. It depends of your Wp them.