Upgrading from ESXi 4 to ESXi 5 can be challenging, especially if you’re using the free version of the hypervisor. That’s because for the free hypervisor, we don’t have the access to the more robust vSphere Update Manager (which makes upgrading very easy).
There are a few options to upgrade a free ESXi 4 hypervisor to ESXi 5. These options are spelled out in the vSphere Upgrade Guide. In this post, I’ll show one method and I’ll mention the other mechanisms. Basically, the options include using vSphere Update Manager (which is available only with vSphere Essentials and higher), performing a scripted upgrade, using vSphere Auto Deploy, using esxicli or using the ESXi 5 CD.