As long as you're using widget depth instead of adjusting the z-position it's fairly easy to upgrade a project. Just to be safe I'd recommend upgrading to 2.7 first and then to 3.0.6. Follow the upgrade notes and use the upgrade tool. I recently updated a large project that was released on the app store from 2.3 to latest in less than 10 minutes. Backup your project before you do and give it a try.