vSphere Update Managerhttp://kb.vmware.com/selfservice/microsites/null
vSphere Update Manager is a software for upgrading, migrating, updating, and patching clustered hosts, virtual machines, and guest operating systems. Update Manager orchestrates host and virtual machine upgrades. If your site uses vCenter Server, VMware recommends that you use Update Manager.
Using vSphere Update Manger, you can perform an orchestrated upgrade. Orchestrated upgrades allow you to upgrade the objects in your vSphere inventory in a two-step process: host upgrades, followed by virtual machine upgrades. For more information, see the Using vSphere Update Manager to Perform Orchestrated Host Upgrades section in the vSphere Upgrade Guide.
Ref: VMware KB: Methods for upgrading to VMware ESXi 6.0