When you install a new version of Solaris software on an existing Solaris system, the installation program lets you choose one of the following options to install the Solaris operating environment:
Upgrade - This option merges the new version of the Solaris operating environment with the existing files on the system's disks. It saves as many modifications as possible that you have made to the previous version of the Solaris operating environment.
Initial - This option overwrites the system's disk with the new version of the Solaris operating environment. You must back up any local modifications that you have made to the previous version of the Solaris operating environment before you begin the installation and restore the local modifications after the installation completes.