We're excited to make the IE8 Release Candidate available today for public download today in 25 languages for Windows Vista, Windows XP, and Windows Server customers. You can find it at http://www.microsoft.com/ie8. Please download it now and try it out. We welcome your feedback!
If you have installed the beta 1 or beta 2 version, also checkout this post : Upgrading to Internet Explorer 8 Release Candidate 1
Source : blogs.msdn.com/ie