Installing/64bit Alpha
The Alpha version does not come with an installer, it's just a Zip file.
That means you have to unzip it (if that wasn't done automatically already), and then place the unzipped app into the proper location.
Mac: Put it into the "Applications" folder
Windows: Put it into the "Program Files" folder. You'll also have to manually create a shortcut, the first time you install. To do that, follow these instructions.