Title :Interactive Installer Existing 5.1 Upgrading to ESXI to 5.5
Scope: ESXI Upgrade from 5.1 to 5.5 in preserving all configuration and settings from previous ESXI 5.1 Host Build Installation.
*ESXI 5.5 ISO
*Previous ESXI 5.1 Host Installation and Configuration.
Interactive Installer Existing 5.1 to Upgrading VSphere ESXI to 5.5 Step by Step Guide.
Upgrade or migrate interactively using an ESXi installer ISO image on CD/DVD or USB flash drive
Upgrade to VMware ESXI 5.5 Video From VMware.
You can run the ESXi 5.5 installer from a CD/DVD or USB flash drive to do an interactive upgrade or migration. This method is appropriate for deployments with a small number of hosts. The installer works the same way for a fresh installation, but if you select a target disk that already contains an ESX/ESXi 4.x, ESXi 5.0.x, or ESXi 5.1 installation, the installer upgrades the host to ESXi 5.5 and gives you the option to migrate some existing host settings and configuration files and preserve the existing VMFS datastore.