Upgrade VMware vSphere

I just managed to upgrade VMware vSphere 5.1 to 5.5. It was really easy and very effective process. First I upgraded the vCenter Server by downloading the latest vCenter Server Appliance and exchanging it with the old one. The step by step process is described here. Then I upgraded the ESXi Server 5.1 to 5.5 from the console by just following the few steps described here. After dowloading the update in zip file, copy it to the ESXi host, connect through sshand execute in the console :

esxcli software vib install -d /vmfs/volumes/<your_volume>/update-from-esxi5.5-5.5_update01.zip