The best way to remove them is to just remove them from the beginning of the array
$myimages = get_field('image_gallery');
for ($i=0; $i<4; $i++) {
// make sure there's still something in the array
// I don't know if array_shift will cause an error on an empty array
if (!empty($my_images)) {
$remove = array_shift($myimages);
}
}
print_r($myimages);