In order to provide running ASP.NET applications which use different ..NET framework versions within single domain, Plesk allows setting up the framework version per virtual (web) directory, where the applications are deployed.
By following these steps you can choose the version of .NET framework for a virtual (web) directory:
1) Click the domain name you need on your home page.
2) Click Web Directories in the Hosting group.
3) Enter the required web directory and click ASP.NET in the Tools group.
4) Select the required .NET framework version and adjust other settings as necessary.
5) Click OK.