You May Try this
if (isset($_COOKIE['remember_user'])) { unset($_COOKIE['remember_user']); setcookie('remember_user', null, -1, '/'); return true;} else { return false;}
Set the value to "" and the expiry date to yesterday (or any date in the past)
setcookie("hello", "", time()-3600);
Then the cookie will expire the next time the page loads.
A clean way to delete a cookie is to clear both of $_COOKIE value and browser cookie file :
$_COOKIE
if (isset($_COOKIE['key'])) { unset($_COOKIE['key']); setcookie('key', '', time() - 3600, '/'); // empty value and old timestamp}