Migrating Flex 3 applications to Flex 4.5 for Adobe Dashboard
Part 1: http://www.adobe.com/content/dotcom/en/devnet/flex/articles/migrating-flex-apps-part1.html

Part 2: http://www.adobe.com/content/dotcom/en/devnet/flex/articles/migrating-flex-apps-part2.html

Part 3: http://www.adobe.com/devnet/flex/articles/migrating-flex-apps-part3.html

Part 4: http://www.adobe.com/devnet/flex/articles/migrating-flex-apps-part4.html