To install or update ESXi 5.5 from usb download the ESXi iso image from vmware.com, download unetbootin-windows-494 – This version allow you to see all drives, just incase you usb drive isn’t detected.
Select Diskimage | ISO and your usb disk, click ok and your done.
If like me you have the Realtek R8168 nic chip you will need to add the driver to the ESXi image.
Download driver/vib Realtek R8168 Esxi 5.5 vib
Download ESXi Customizer