Oracle12c Upgrade Workshop
http://gavinsoorma.com/2013/07/12c-database-upgrade-11-2-0-3-to-12-1-0-1-upgrade-using-dbua/
http://ronr.blogspot.in/2013/06/upgrade-oracle-grid-infra-structure-gi.html
http://db12c.blogspot.in/2013/06/upgrade-oracle-database-11203-to-121010.html
http://db12c.blogspot.in/2013/06/upgrade-oracle-database-11203-to-121010.html
http://www.oracleangels.com/2013/08/steps-to-upgrade-11203-to-12101-grid.html
http://asanga-pradeep.blogspot.in/2013/07/upgrading-from-11gr2-11203-to-12c-12101_9.html