How to change ASP.NET version in IIS 7
1. Clich on Start Menu, Control Panel, Administrative Tools, Internet Information Services (IIS) Manager.
2. Click on Application Pools, and locate the application pool for your web site.
3. Right click on the application pool and click on Basic Settings.
4. Change the ASP.NET version from the drop down menu under .NET . . . → Read More: How to change ASP.NET version in IIS