To download D5 Lite for SketchUp and start using features like LiveSync you'll first need to install the D5 Launcher.

The launcher acts as a hub to manage projects and downloads, with news for events, webinars and updates. But the bit we're focusing on is found at the top of the page under Products. Alternatively you can go to Workflow on the left and then Lite.

Once installed go to SketchUp and you should see a tool bar with the D5 tools. You will need one of the first two icons. 

The coloured icon will connect your SketchUp file to D5 Render.

The black and white icon will load D5 Lite giving you an extra window showing you a rendered view of your SketchUp file.  To turn this rendered view of your model to real-time you will need to activate 'Sync Viewport'.