The Developer Preview has already had updates through Windows Update.
Chances are you won't be able to upgrade it to the beta version, a clean install will be needed.
Below are some of the updates from Windows Update for the Developer Preview.
1. Applications stop responding when they send synchronous messages to a suspendedapplication that is created for Windows Developer Preview
2. On a computer that is running Windows Developer Preview (codenamed "Windows 8"), input text that should display right-to-left in Internet Explorer is mirrored.
3. Windows Store client crashes at startup in Windows Developer Preview
4. Update fixes lack of notifications and restart problem with multiple image tile templates in Windows Developer Preview
5. Windows Developer Preview still consumes battery power when Windows Developer Preview moves from sleep mode to hibernation
6. An update is available for two issues that occur when you log on to a computer that is running Windows Developer Preview:
Issue 1
When you log on to a computer that is running Windows Developer Preview, a blank green screen appears. However, the start screen should be displayed.
Issue 2
When you log on to a computer that is running Windows Developer Preview, you cannot use the keyboard to move through the Tile grid and select an application or Tile.
