You would work your way back through the security guide discussion on enabling kerberos:

http://www.cloudera.com/content/cloudera/en/documentation/cloudera-manager/v5-latest/Configuring-Had...

Note that if HBASE, or NN HA or JT HA was configured after enabling security, the cleanup can be difficult, the Znode paths within zookeeper might require manual removal of the ACL statements.

Todd