So how can I upgrade 1.52 to 2.0RC?
Currently there's no support here for 2.0 as it's beta/rc software, and needs to be installed/used on a use at your own risk basis.
If you dare, and you really want to maybe this post will help you. Please be certain you have read the thoughtfully lengthy disclaimer several posts down.
I'm not a member of the support team, or the development team (so important you know that, take everything i say with a tablespoon of salt please) but so far, all my themes are fine. Well.. as fine as they were before anyway.