Here we will see how to upgrade ESXi host from 4.0.0 U1 to 4.1.0 using ESXi tech support mode.
we will need the update bundle which is a zip file.
Also you will have to enable SSH so that you can upload the .zip bundle to ESXi host.
We will use WinSCP and Putty as our tools to connect to ESXi host.
As you can see below I have the bundle zip file. 
Lets upload the file to ESXi using winSCP utility. 
You can see I have uploaded the file in “datastore1”, now lets rename it to 40-41.zip so that it will be easy when we refer to this file in SSH CLI
Open Putty, connect to ESXi host.
Login using root username and password
We will use “esxupdate” cmd
esxupdate is found in /sbin directory. 
Let us check the bundle file which we uploaded in datastore1 
We will need the location of file, so we will highlight the location i.e., /vmfs/volumes/4e4….d42 and right click, which will copy the location to clipboard.
Lets run the esxupdate cmd 
The ESXi host should be in maintenance mode for update to run successfully, and I forgot to put it which gave me the error as shown below.
You will also notice that I have used the “datastore1” in the URL, which also works as it’s the shortcut to the numerical folder that we saw before. 
Lets put the host in maintenance mode using vim-cmd hostsvc/maintenance_mode_enter 
Let us run the esxupdate cmd again. and you can see the update has started. 
The update is completed, as the message says we will reboot the host using “reboot” cmd. 
Updated to 4.1.0. 
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