First, download the new beta installer from the downloads section of the website.

It is recommended you do this BEFORE deleting your old install so you can preserve macro's/settings.

Once you have completed the download you will have a folder that contains a file called Install. Run it as admin. Wait 30-60 minutes.

It will ask you if you have windows 7/8/8.1 or not. If so, press Y. If not, press N.

Then there will be a launcher icon on your desktop. That launches the game.