Take a look at official documentation: About the vCenter Server Appliance 6.0 Upgrade Process
And here is a good step by step guide: http://anthonyspiteri.net/vsphere-6-0-vcenter-server-appliance-upgrading-from-5-x/
i've wrote an article on my blog, which discribes the Upgrade.
After that you can also deploy the first Update to vCSA 6.0.0b
Hope you didn't migrate your vCSA from a vCenter Server for Windows installation. Then the Upgrade will fail with "vPostgres first boot error"
Hoping you may find this useful.
Please find the steps with screenshots for vCenter Server Appliance (VCVA) Major upgrades from 5.5/5.1 to 6.0x from following link:
Step with Screenshots for fresh install of vCenter Server Appliance (VCVA) 6.0x: