Download addons package Microsoft Silverlight 4 and RIA Services tools for Microsoft Visual Studio 2010. You can install them in either Visual Studio 2010 or Visual Web Developer 2010 Express.
It extends existing Silverlight 3 features and multitargeting capabilities in Visual Studio 2010 to also create applications for Silverlight 4 using C# or Visual Basic. These addon tools add support for targeting Silverlight 4 in the Silverlight designer and project system.
Download package include tools: Silverlight 4 developer runtime Silverlight 4 SDK (software development kit), Update for Visual Studio 2010 and Visual Web Developer Express 2010, Silverlight 4 Tools for Visual Studio 2010, WCF RIA Services V1.0 for Silverlight 4 and F# Runtime for Silverlight 4.