If you have installed the Drag[en]gine and/or IGDE using repositories or market place updates arrive automatically.
Otherwise get the 1.3 release files from the Download Section. You can install it over the 1.2 release but it is recommended to uninstalling 1.2 first to keep the game engine directory clean.
To develop games you do not need the game engine source code nor compiling anything. Just install the IGDE, create a project, run and distribute to *.delga file and you are done.
You can find the full Changelog of the latest release on this Perma-Link:
Changelog Latest Release
Some of the new Features (besides others) are these.
Added new convenience methods to DragonScript language and added support for run-time optimizing functions as preparation work for JIT support.
Added GlobalEvents for those used to work with global events in addition to Behavior Elements
Added Renderable Panel behavior complementing Renderable Canvas behavior. This simplifies using the full power of the UI ToolKit for dynamic skins in behavior elements. Managing dynamic texture content never has been easier than this.
If you have questions, suggestions or other inquiries you can PM me here or stop by the Discord Channel.