Download it here.

Read about it in these blog posts:

Somasegar: Visual Studio 2012 and .NET 4.5 Release Candidates available now!

Jason Zander: Announcing the Release Candidate (RC) of Visual Studio 2012 and .NET Framework 4.5

Brian Harry: Visual Studio/TFS 2012 Release Candidate Available Today

And check out the Visual Studio 2012 RC documentation here.