How can you remove .NET Framework 4.5 Beta (either manually or using a cleanup tool)?
Given that the framework installs new assemblies into the Global Assembly Cache and other locations within your Windows directory I would advise against a manual uninstallation. Why can you not uninstall via the proper channels in Programs and Features?
Note that .net 4.5 essentially overwrites any previous .net 4.0 installation. So once you remove it you will have to reinstall .net 4.0