You can upgrade vCenter and components separately to customize the location and configuration of the components. The standalone vCenter Single Sign-On deployment contains only one vCenter Single Sign-On node.
For most standalone vCenter Single Sign-On deployments, with all components on the same host machine, you can upgrade vCenter Single Sign-On, the vSphere Web Client, vCenter Inventory Service, and vCenter Server together on a single host machine using the vCenter Server Simple Install option.
See Use Simple Install to Upgrade vCenter Server and Required Components.
Note: vCenter Server 5.5 supports connection between vCenter Server and vCenter Server components by IP address only if the IP address is IPv4-compliant. To connect to a vCenter Server system in an IPv6 environment, you must use the fully qualified domain name (FQDN) or host name of the vCenter Server. The best practice is to use the FQDN, which works in all cases, instead of the IP address, which can change if assigned by DHCP.