Platon is a HTML5, responsive and mobile-friendly theme.
Platon 1.x is a subtheme of Open Framework. Make sure to first download Open Framework and copy it to your theme folder.
Platon 2.x is completely stand-alone and can be used as is.
Platon 3.x splits the page layout in smaller templates, allowing easier extension for sub themes.
Update from 2.x to 3.x
Replace all files as you usually would, then make sure to clear your cache. If you already created a sub theme for 2.x, consider updating it to using the 3.x logic. It will not break, however. Your sub theme will still look fine.