If you have Windows 7 RC or Windows 7 Beta or any other pre-release leaked version then you cannot directly upgrade it to Windows 7 RTM build 7600.16385 as it is not supported by default.

Microsoft recommends Windows 7 beta or RC users to perform a clean or fresh installation of Windows 7 RTM, and use Windows Easy Transfer to save and transfer user accounts, Windows settings, program settings, personal customizations and files from current installation to newly installed Windows 7 RTM system.

When you try to upgrade to Windows 7 build 7600.16385, The setup will stop loading and give you an error message saying : You cannot upgrade this prerelease version of Windows 7. Go online to see how to install Windows 7 and keep your files and settings.

Windows 7 RTM is so build that it blocks and prevent upgrade from all pre-release versions of Windows 7 earlier than build 7233 for client edition, including Windows 7 Beta Build 7000 and Windows 7 RC Build 7100. But, perform this hack to upgrade in-place and bypass the error message.

1. Extract the contents of Windows 7 RTM ISO Image to any folder or USB Disk using WinRAR.
2. Find the file cversion.ini in a text editor such as Notepad.
3. Modify the MinClient build number to a value lower than the down-level build. For example, change 7233 to 7000.
   Original content of cversion.ini:

   [HostBuild]

   MinClient=7233.0

   MinServer=7100.0

   Change it to:

   [HostBuild]

   MinClient=7000.0

   MinServer=7100.0

4. Save the File with Original name and Location.
5. Continue installation with this modified setup.
6. Choose “Upgrade” type installation to have in-place uprade to Windows 7 RTM ISO Gold. The version check will be skipped and bypassed.