Funny question but I stacked on it. I opened in VS2013 solution file which uses VS2012, but it still doesn't show me any screen for upgrade solution to VS2013. I mean I can open this project in VS 2013 and it works but solution file still shows that it use VS2012
According to this article some wizard should be shown, but it doesn't http://msdn.microsoft.com/en-us/library/vstudio/ms185327(v=vs.100).aspx