I did an upgrade from vSphere ESXi 4.1 to ESXi 5.0 using the ESXi 5 installation CD. The upgrade process was very easy.. elapsed time: 10 minutes!
^ Current installed OS: VMware ESXi 4.1.0 build 260247
– Mount the vSphere 5.0 cd-rom in the host
– Boot from CD-Rom drive
– Choose: ESX-5.0.0 Installer in the menu
– Press: Enter to continue the installation
– Accept the EULA – Press: F11
– Select the disk to with the existing ESXi 4.1 installation
– The setup detects there’s an older version of vSphere installed, select in the menu what to do:
The selected storage device contains an installation of ESXi and a VMFS datastore. Choose whether to upgrade or install and overwrite the existing ESXi installation. Also choose whether to preserve or overwrite the existing VMFS datastore.
( ) Upgrade ESXi, preserve VMFS datastore
( ) Install ESXi, preserve VMFS datastore
( ) Install ESXi, overwrite VMFS datastore
– Confirm Upgrade: Press F11 to start the upgrade process
– Upgrade is started…
– Upgrade Complete!
ESXi 5.0.0. has been successfully installed.
ESXi 5.0.0 will operate in evaluation mode for 60 days. To us ESXi 5.0.0. after the evaluation period, you must re-apply your licenses to this server. To administer your server, use the vSphere Client or the Direct Control User Interface
Remove the installation disc before rebooting
Reboot the server to start using ESXi 5.0.0
Final result: Successfully upgraded from ESXi 4.1 to ESXi 5.0