Last week I upgraded VMware vCenter 5.5 server (based Windows 2012R2) at the company environment I work for, the upgrade was very simple.
Pre-install: Please check article “Minimum requirements for the VMware vCenter Server 6.x Appliance (2106572)”
– Select: Install
– Select: Next
– Select: “I accept the terms of the license agreement” > Next
– Fill in vCenter Single Sign-On password > Next
Warning: You Microsoft SQL Express database will be migrated to VMware vPostgres. If you would like to continue using Microsoft SQL, see install/upgrade documentation about migrating to full SQL Server
– Leave the ports to configure default > next