Doing an in-place upgrade of Citrix StoreFront one weekend and was greeted with the error:
"StoreFront cannot be upgraded because the following folders are in use by another program. Close the program and try again."
Citrix StoreFront 7 1912 CU1
Take note of the folder or file that was mentioned in the error. In my case, it was c:\inetpub\wwwroot\Citrix\StoreWeb.
Using Microsofts process explorer, press Ctrl + F and enter the path in the error.
Find the offending process and stop it, then try the upgrade again.
In my case it was Explorer. I ran AutoSelect from the Citrix ISO, then I ended explorer using task manager and continued with the installation. After the installation, I started Explorer again using task manager.