I've just found the answer, maybe it helps someone of you, too:

You can replace the old card with the new one like so:

$customer = \Stripe\Customer::retrieve($client_id);
$customer->default_source = $token;
$customer.save()

I've just found the answer, maybe it helps someone of you, too:

You can replace the old card with the new one like so:

$customer = \Stripe\Customer::retrieve($client_id);
$new_card = $customer->sources->create(array("source" => $token));
$customer->default_source = $new_card->id;
$customer->save();