Remove a cookie

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.

To reliably delete a cookie it's not enough to set it to expire anytime in the past, as computed by your PHP server. This is because client computers can and often do have times which differ from that of your server.

The best practice is to overwrite the current cookie with a blank cookie which expires one second in the future after the epoch (1 January 1970 00:00:00 UTC), as so:

setcookie("hello", "", 1);

A clean way to delete a cookie is to clear both of $_COOKIE value and browser cookie file :

if (isset($_COOKIE['key'])) {
    unset($_COOKIE['key']);
    setcookie('key', '', time() - 3600, '/'); // empty value and old timestamp
}