Amendment in GST Registration

Hello friends kindly help me out in this case:

Assesse got registered under GST act, with old PAN name now he got his PAN updated. Can you tell me how to update the same in GST. There was a notification on the site that portal will be open for amendment in a week notification was dated 18th July, 2016.
Another thing is when I googled for this query I got to know that GST Form 14 is to be used for any changes in registration and it shall be digitally signed. But when I searched for that form it was for cancellation of registration and also it was available in PDF format.

kindly let me know how can I updatemy registration.