From the news:
Lucene can be downloaded from http://www.apache.org/dyn/closer.cgi/lucene/java/5.2.0 and Solr can be downloaded from http://www.apache.org/dyn/closer.cgi/lucene/solr/5.2.0
…
See the Lucene CHANGES.txt and Solr CHANGES.txt files included with the release for a full list of details.
Enjoy!
PS: Also see the Reference Guide for Solr 5.2.