I would be careful about upgrading to DP 8, it is using an entirely new IDB which has had 'issues'. I would advise upgrading to DP 7, and installing the 7.03 patch bundle if you do not need the functionality of DP 8
Having said that, you can find the Installation and Licensing Guide for DP 8 at the URL:
Chapter 4 is about upgrading from a pervious version to DP 8