How do I enable addons/update the client on the MoP beta?

So from what I've read addons were enabled on the MoP beta a week ago or so, but for me there is still no addon button when I log in. I just finished downloading the client yesterday and it says I'm running version: 5.0.1 (15799) (Beta x64) Jun 27 2012.

I read somewhere else a suggestion to update the client but I have no clue how to do this, I've looked everywhere!