Introduction
Welcome to the CentOS 6.7 release. CentOS is an Enterprise-class Linux Distribution derived from sources freely provided to the public by Red Hat1.
CentOS conforms fully with Red Hat's redistribution policy and aims to be functionally compatible. CentOS mainly changes packages to remove upstream vendor branding and artwork.
Similar to the practice of the upstream vendor, there is no supported path to 'upgrade' an installation of a prior major CentOS release (presently CentOS 5) to a new major release. This is not a CentOS imposed limitation, but rather reflects the upstream's approach on this matter. People who feel adventuresome and want to experiment are reminded to take and test backups first. As a note to people who attempt the upgrade in spite of this warning, such as by the unsupported upgradeany option from the media install command line, please note that you will need to manually retrieve the current centos-release package, manually do a rpm -e --nodeps removal of the prior centos-release package, and then manually install the CentOS 6 centos-release package, before yum can have any chance of working properly.
The Continuous Release (CR) repository makes generally available packages that will appear in the next point release of CentOS, on a testing and hotfix basis until formally released.