There isnt a direct upgrade process for App Volumes but the process is fairly simple, it needs to be removed first then reinstalled while using the same database. The following will illustrate the upgrade process from v2.9 to 2.10.

App Volumes 2.10 release note are found here

First remove App Volumes from the App volumes server, leave Unmount all attached volumes clear

Run the install setup.exe from the downloaded media and choose Install App Volumes Manager

Choose the SQL instance and database. I am using SQL express on the local server and using the default DB name of svmanager_production, if the name of the original database is different make sure this matches. Make sure Overwrite existing database is clear. Choose the relevant ports App Volume agent will use

Choose the install directory and Install

Once complete log into the management page using the same admin account as before. Check the configuration is correct and the AppStacks are still available

It is also a good practice to upgrade the templates used for AppStack and Writeable Volumes

You must also update the agent on the desktops.