1. First you need to log in to a machine that has the VMware vSphere CLI installed.

2. Download the following upgrade ZIP bundles from the VMware Web site to a location that is accessible to the vSphere CLI machine.

The esxupdate bulletin, pre-upgrade-from-ESX4.0-to-4.1.0-0.0.build#-release.zip
The upgrade bulletin, upgrade-from-ESX4.0-to-4.1.0-0.0.build#-release.zip

3. Power off any virtual machines that are running on the host and place the host into maintenance mode.

4. Install the esxupdate bulletin by running the following command on the vSphere CLI machine.

vihostupdate.pl -i –server <host name or IP address> –username <username> –password <password> -b <location of the ESX update ZIP bundle>

5. Install the upgrade bulletin by running the following command on the vSphere CLI machine.

vihostupdate.pl -i –server <host name or IP address> –username <username> –password <password> -b <location of the ESX upgrade ZIP bundle>

6. Verify that the bulletins are installed on the ESXi host by running the following command.

vihostupdate.pl -i –server <host name or IP address> –username <username> –password <password> –query

7. Reboot the host.