How do I upgrade to Fusion 13.5

[Technogeezer]

You're asking a pretty general question.

If what you're asking "how do I install the software",  I'd recommend

• Read the Fusion 13.5 release notes https://docs.vmware.com/en/VMware-Fusion/13.5/rn/vmware-fusion-135-release-notes/index.html and make sure you understand the changes that have been made to the release. In particular, look at any linked documents in the notes.
• Make sure your Mac meets the system pre-requisites.
• Make sure you have a Fusion 13 license (either purchased or personal use license).
• Download VMware Fusion 13.5 from VMware https://customerconnect.vmware.com/downloads/info/slug/desktop_end_user_computing/vmware_fusion/13_0
• Shut down (do not suspend) your VMs and remove any snapshots.
• Quit Fusion and copy your VMs to another drive - always good to have a backup before any changes in Fusion and macOS
• If running a Tech Preview version of Fusion, move VMware Fusion Tech Preview.app found in your Applications folder to the trash.
• Install Fusion 13.5 by opening the downloaded disk image file and following the instructions.  
• Your existing VMs should continue to work on Fusion 13.5

If you're asking about licensing

• Fusion 13 licenses work on Fusion 13.5 (both paid and personal use licenses).
• If you have a paid license for any Fusion versoin prior to 13, you'll need to purchase a new Fusion 13 license. You may be eligible for upgrade pricing if you had a paid license for Fusion 11 or 12.
• If you have a personal use license for Fusion 12, you'll need to register for a new personal use license for Fusion 13. https://customerconnect.vmware.com/evalcenter?p=fusion-player-personal-13