• Download the SDK from the Gumbo Downloads page. The file will be called something like ‘flex_sdk_4.0.0.xxxxx.zip’.
  • Unzip and move the resulting folder to /Applications/Adobe Flex Builder 3/sdks/ and rename it to 4.0.0
  • In Flex Builder, go to Preferences -> Flex -> Installed Flex SDKs. Click the Add… button and add your new 4.0 SDK to the list. If you like you can click the checkbox next to the new SDK and uncheck the others, to enable it by default. Flex Preferences
  • To update your project so it uses the new SDK, go to Project in the Flex Builder top menu, then select Properties -> Flex Compiler, and update the Require Flash Player Version: to Project Preferences You should now be able to use some of the great new stuff from Flex 4, such as the new VideoPlayer component :
<?xml version="1.0" encoding="utf-8"?>

    autoPlay="false" />