In most cases the preview would be installed clean not simply having replaced a working previous version like 7 on a machine but installed to a separate partition or drive if not on a VM. Here I tried it on both VM Players I had onhand as well as downloading the latest plus VBox and one other VM program but still never got to the physical drive install.
I wouldn't expect any auto update on a VM to start with while the Windows icon appeared on the task bar in June for reserving the free copy. Most likely a clean install of 7 to proceed that to be upgraded over will need to take place since I won't be allowing 10 to replace the 7 host install. The present copy of 7 on the host drive is now 2yrs, old having put that on in mid June 2013 replacing the image restored copy of the 2010 7 install on this build which had replaced that older build I beta tested 7 on which previously ran Vista. Kind of a chain gang effect.