We can use the following code in place of the_content() to remove first image
echo preg_replace("/\< *[img][^\>]*[.]*\>/i","",get_the_content(),1);
or we can use hook to remove from the_content as following:
put the following add_filter before the_content in any file you want to remove image
add_filter('the_content', 'remove_image_content'); the_content();
or you can put filter on functions.php to remove first image from all the_content
add_filter('the_content', 'remove_image_content');
And put the following function on functions.php
function remove_image_content($content) { return preg_replace("/\< *[img][^\>]*[.]*\>/i","",$content,1); }