More importantly than the VS version is the ASPDNSF version. If you are going from < 9 there is more work involved in getting rid of the Component Art Menu and other skin changes due to the change to master templates. Also in the current version (v9.4.1) there is more skin work as they default skins are now responsive (YEAH!).
This link covers most of what you need to know at a basic level: http://manual.aspdotnetstorefront.com/p-948-upgrading-to-a-9x-version.aspx