I almost made up my mind to delete everything, format and reinstall windows 7, based on recommendations from Microsoft but this link was very handy.
With one file name change, I was able to upgrade from Windows 7 RC and Windows 7 RTM. I hope I don't face any problem later :)
I did not even burn a DVD. I extracted iso file on a folder using 7-zip and changed content in the file source\cversion.ini file and modified MinClient parameter to 7100.0