You can create an ESXi host upgrade baseline by using the New Baseline wizard. You can create host baselines with already uploaded ESXi 6.0 images.
You can upload and manage ESXi images from the ESXi Images tab of the Update Manager Administration view.
Update Manager 6.0 supports upgrade from ESXi 5.x to ESXi 6.0. Host upgrades to ESXi 5.0, ESXi 5.1 or ESXi 5.5 are not supported.
Before uploading ESXi images, obtain the image files from the VMware Web site or another source. You can create custom ESXi images that contain third-party VIBs by using vSphere ESXi Image Builder. For more information, see Using vSphere ESXi Image Builder .
If your vCenter Server system is connected to other vCenter Server systems by a common vCenter Single Sign-On domain, and you have more than one Update Manager instance, host upgrade files that you upload and baselines that you create are not applicable to the hosts managed by other vCenter Server systems. Upgrade files and baselines are specific for the Update Manager instance you select.