The install process of vCenter 6.0 is not completely obvious as its not an OVA-file to deploy so I decided to write this quick guide on how to upgrade vCenter 5.5 to 6.0
1. Download the ISO
go to the vmware download page (https://my.vmware.com/web/vmware/details?downloadGroup=VC600&productId=491&rPId=7501) and fetch the ISO file called VMware vCenter Server Appliance and download it to your computer.
2. Mount/Extract the ISO
Next step is to mount the ISO. If you are running Windows 8 you can just right click it and chose "mount" to have it mounted to a virtual cd-drive. Else you can use WinRAR or 7zip to extract the files from the ISO.
3. Upgrade the VMware Client Integration Plugin
On the ISO, find the folder named "vcsa" and inside it you find an installer for upgrading the VMware browser plugin on your computer to 6.0. Remember to close all open browsers first, then run the installer.
4. Start the upgrade
When the browser plugin is upgraded go back to the ISO, in the root you find a file called vcsa-setup.html, open it with your browser and chose "Upgrade".
Accept the EULA and countine.
The first info the installer needs is the target server and credentials. Note that this is the target ESXi-host for where you want to install your vCenter 6.0 VM, NOT your current vcenter server.
5. Source Appliance
The next step is to chose a name for you new vcenter server and then go ahead and enter all the login info for your old vcenter server and the esxi-host that it is currently deployed on.
When you have entered all the login details you will have to chose the size of your vcenter installation (how many hosts and VMs it should be able to manage) and what datastore to put it in.
The last step will be to assign an IP address to the new vcenter installation from which it can reach your old vcenter. Note that this address will only be used temporary, as soon as the install is complete your old vcenter will be deleted and the new install will start using the same address as your old install.
This was the last step, now your upgrade will begin, this process takes a fairly long time, atleast 15min+ so have patience.
As soon as the upgrade is complete you then can go ahead and login to your new vcenter 6.0 via the new fast web client.
Hope you had some help from this guide.
