You can find the full announcement including a link to he new certificate here: https://developer.apple.com/news/?id=7gx0a2lp
Your servers will need the new root certificate in order to be able to trust the APNs servers. To ensure a seamless transition and to avoid push notification delivery failures, verify that both the old and new root certificates for the HTTP/2 interface are included in the Trust Store of each of your notification servers before March 29.
You can add the new root certificate to your Trust Store at any point before the deadline, and do not have to wait until March 29th to do so.
Note that Apple Push Notification service SSL provider certificates issued to you by Apple DO NOT need to be updated at this time.
Please respond in this thread if you have further questions.