June 26, 2014: For information on what's new in 0.8.0 (Beta), see the release announcement.
You cannot patch-update to 0.8.0 from older versions: you will need to install a fresh build.
The official download links and documentation are here:
You can also download simple .zip installations as is offered for other individual builds here:
Windows: http://dl.google.com/dl/android/studio/ide-zips/0.8.0/android-studio-ide-135.1245622-windows.zip (161 MB)
Mac: http://dl.google.com/dl/android/studio/ide-zips/0.8.0/android-studio-ide-135.1245622-mac.zip (161 MB)
NOTE: These .zip files do not contain an embedded SDK install. If you have an existing install of Studio which contains an embedded SDK, if you upgrade by installing one of these zips, make sure you copy over the SDK as well.