I want to integrate papal with my site, so that when a member makes a payment via paypal they immediately gets upgraded to premium plan on successful payment. I used this to make pay now button for my site https://merchant.paypal.com/cgi-bin/marketingweb?cmd=_render-content&content_ID=merchant/wp_standard but i want the membership status to change as well as soon as the payment makes through. Can anyone please help me.
You'll need to make use of the paypal IPN (Instant Payment Notification). Take a look at this tutorial http://designertuts.com/paypal-ipn-receiving-instant-payments-in-your-web-application/ Basically, it sends the data to a script on your website when the payment is made, and the script should then update the users account level. If your site is PHP, i can help you, just shoot me a PM
Depending on what your site uses, there may be a plugin you can use. Most forum software has at least one.