How do I delete PHPSESSID on client computers

Question

UPDATE ON THE PROBLEM:

• On some browsers, we have two PHPSESSIDs.
• One PHPSESSID is not set by me anywhere in my script
• It has

Answer 1

I would simply expire the cookie from /folder. This should leave you with only one session cookie for /

setcookie('PHPSESSID', '', time() - 86400, '/folder/');