How To Upgrade VMware ESXi 3.5 To 4.1 Update 1 (Free Version)
In this guide I will show you how to upgrade VMWare ESXi 3.5 to ESXi 4.1 Update 1 (Free Version) without going through the pain of reinstalling your host server and then restoring your VMs.
Read more: http://www.howtoforge.com/how-to-upgrade-vmware-esxi-3.5-to-4.1-update-1-free-version