Now we may go for vmware 6 version migration as suggested by vmware.
How to make a plan of action
I need all your help.
The first steps are to ensure that all the ESXi hardware is supported by the new version, and any add-on and/or 3dr-party tool that you use (e.g. backup) supports the new version too. Once all the prerequisites are met, plan the upgrade according to the Upgrade Guide that can be found at https://www.vmware.com/support/pubs/vsphere-esxi-vcenter-server-6-pubs.html
There might be other things to consider too, e.g. whether you want/need to run vCenter Server on a new Server (e.g. 2008 -> 2012), or whether you want to migrate from the Windows version to the vCenter Virtual Appliance.
It is necessary to update to windows server w2k12? I am reading the doc and it said that will work on w2k8.
on the other hand I usually update my ESXi physically, I know that is it is possible with vmware update manager but I tried sometimes and always problems, so I usually shut down the VM machines and update one by one all ESXi with the CD media.
Personally I prefer on this way, It is true, that my environment is not too big just 3 ESXi and 10 VM servers and computers... :smileyblush:
You can install vCenter 6 on windows 2008 x64. If you have vCenter 5.5 running on windows 2k8 you can upgrade it to vCenter 6.
Update manager is best choice to upgrade esxi host and its easy. Start the upgrade process and seat back.