Change my website from PayPal Adaptive payments to express checkout -- 2

Website is currently out of date using Adaptive payments to do chained payments. I want to remove adaptive payments completely and use express checkout with GUEST PAYMENTS enabled! How my website works: [login to view URL] is a PHP script (MADE IN PHP CORE) which I got from a good friend back in 2015. It runs on PHP 5.4 and is out of date because it uses adaptive payments to do split payments so site owner could collect fees. I want to take this feature out and replace it with express checkout. Website should still work the same way and IPN should still be used to confirm payment with the website. Take a look for yourself: product URL: [login to view URL] Here is a test product, how it used to work was: 1. Customer would come to page and press buy now 2. Pressing buy now would generate a payment key which would be UNIQUE to its session 3. after few seconds redirect to paypal for checkout 4. after checkout IPN notification and then customer notified of product code by email WHICH IS SENT TO THEIR EMAIL THEY ENTERED ON PAYPAL (IMPORTANT) which will allow them to download their item at [login to view URL] Paypal checkout must allow guest checkout (user does not need to create a paypal account, they can pay with credit card) If you can do this job quick fast and cheap hit me up. Thanks. If you can do this i will send you my cpanel information so you can look it up and check if you can do it (only if i see you fit as a person to work on my site)