First of all take into account that the product team is working on Prism v4, so you could download the latest version from
Regarding to your question, there is no guidance on this topic in Prism v2.2 out-of-the-box. But you need to install all System Requirements listed on the readme.txt which is part of Prism 2.2.
As the documentation says that this is a minor update of Prism, which allows you to use Silverlight 4.
A possible scenario is that if you change your existent project to target SL4, you will receive the following error when you open project in Visual Studio:
Unable to read the project file: The imported project “C:\Program Files\MSBuild\Microsoft\Silverlight\v3.0\Microsoft.Silverlight.CSharp.targets” was not found. Confirm that the path in the <import> declaration is correct, …
Therefore, you should modify the <Import> path in the project files (files ending with*.csproj) to point to the Silverlight 4 installation path. For example:
Then you should reference the new assemblies in that release. A part from this, it should not represent any other inconvenient when migrating from the previous version.
If you need guidance on what assemblies are required, you could check the references of the Stock Trader Reference Implementation.