If you want to update your vCenter Server Appliance 6.5 (VCSA) there are many ways, here is one I use the most.
Note: Before you start updating check all dependencies and interoperapilities! ESXi, vSAN, NSX, Horizon,vRealize and a lot of other VMware products as well as all 3rd party products using APIs and Interfaces of the vCenter that can be changed during the update.
Open a browser, then go to the VCSA VAMI (https://yourvcenterfqdn:5480) and login as root. In the left pane select Update, now use the „Check Update“ button and select „Check Repositoty“ to get the latest update from the internet.
Note: If your VCSA has no access to the internet, you can download the Update ISO at the VMware site. Make sure you got the Full Patch ISO file -> „VMware-vCenter-Server-Appliance-6.5.0.xxxxx-xxxxxxx-patch-FP.iso“. Attach it to your VCSA, go to VAMI , use „Check Update“ button and select „Check CDROM“.
Now you can hit the „Install Updates“ button and follow the wizard.
Wait for installation to complete.
After the installation completed successfully, you need to reboot the VCSA manually.
Go to „summary“ klick „reboot“ in the upper right corner and acknowledge the reboot with „yes“.
One last doing before the update is realy finished. When the VCSA is rebooted and the VAMI available again login as root. Check under „Administration“ that „Root password expires“ is set to „No“.
Now the VCSA is up to date and you can use it as always!
After that you can update your ESXi Hosts, maybe vSAN and other VMware products that require a certain VCSA version.