I don't know of any upgrade instructions but checking the change log might help a bit.
http://svn.apache.org/viewvc/nutch/branches/branch-1.2/CHANGES.txt?view=markup > Hello everyone. > > I currently have Nutch 1.0. I would like to upgrade to the latest version > 1.2. > How do I upgrade? Are there any instructions detailing how to upgrade?
