How do I select ASP.NET 3.5 via the Control Panel?

Programming > ASP.NET
ASP.NET 3.5 was an upgrade of ASP.NET 2.0.  By selecting V2 in the control panel you will be selecting ASP.NET 3.5.
The same is true for ASP.NET 4.5. Selecting ASP.NET 4.0 will provide access to  ASP.NET 4.5 for your site code if it requires it.