New .NET Framework on next update

I have an existing application built in .NET framework 3.5, I have upgraded the application to .NET Framework 4.0 to add new features, How can I use automatic updater to also check if the user has .NET 4.0 installed so the app won't crash when it updated via Wybuild. Thanks!

Create & execute a boostrapper that checks if the .NET 4.0 is installed, and if not download and install it.