VMware provides many options to upgrade to vCenter Server 6.5.
You can upgrade or migrate your vCenter Server version 5.5 or version 6.0 installation to version 6.5 using the method that best addresses your deployment goals and requirements.
High-level steps for upgrading or migrating vCenter Server:
Select your upgrade goal.
Verify that your system meets the hardware and software requirements.
Prepare your environment for the upgrade or migration.
Upgrade or migrate your vCenter Server for Windows or vCenter Server Appliance deployment.
Complete any required post-upgrade or post-migration tasks.
You can connect vCenter Server instances with external Platform Services Controller instances in an Enhanced Linked Mode configuration.
Although you can choose to join a vCenter Single Sign-On domain, you should consider vCenter Server with an embedded Platform Services Controller as a standalone installation and do not use it for replication of infrastructure data.
Concurrent upgrades are not supported and upgrade order matters. If you have multiple vCenter Server instances or services that are not installed on the same physical server or virtual machine (VM) as the vCenter Server 5.5 instance, see Distributed vCenter Server 5.5 for Windows Services Relocation During Upgrade or Migration. For information on upgrade order for transitional environments, see Upgrade or Migration Order and Mixed-Version Transitional Behavior for Multiple vCenter Server Instance Deployments.
vCenter Server Supported Upgrade Methods
Graphical User Interface (GUI) Installer
The GUI installer provides a two-step upgrade method using OVA and the vCenter Server Appliance Management GUI. The first step deploys an unconfigured Platform Services Controller appliance or vCenter Server Appliance as an OVA file. The second step uses the vCenter Server Appliance Management GUI to configure the new appliance using the source deployment data.
Command Line Interface (CLI) Installer
The CLI installer provides advanced users with a CLI method for upgrading the vCenter Server Appliance or migrating vCenter Server on Windows to an appliance. You can upgrade or migrate to vCenter Server Appliance configurations using customized CLI templates.
Migration Assistant Interface for Migrating vCenter Server on Windows to vCenter Server Appliance
When you migrate a legacy vCenter Single Sign-On, Platform Services Controller, or vCenter Server on Windows to an appliance using the Migration Assistant interface. You can use either the GUI method or the CLI method to migrate the legacy Windows installation data to a target appliance. See Overview of Migration from vCenter Server on Windows to an Appliance.
Deprecated vCenter Server Deployment Models
When upgrading or migrating from deprecated deployment models, you must first migrate your deployment to a currently supported deployment model before attempting to upgrade or migrate it to a vCenter Server 6.5 deployment. For more information, see Moving from a Deprecated to a Supported vCenter Server Deployment Topology Before Upgrade or Migration
Patching and Updating vCenter Server
A patch or update brings the vCenter Server 6.5 software up to the current minor version on the existing physical or virtual machine. You can use the patching process to make minor upgrades to your 6.5 deployment. See Differences Between vSphere Upgrades, Patches, Updates, and Migrations and Patching and Updating vCenter Server 6.5 Deployments.