To run different .Net Framework versions from your application pool,
you shall create a virtual directories and assign the mentioned application pool
(virtual directories) as different .Net Framework version.
3. Click on "Web Sites" under "Web & Applications" to proceed to the next step .
4. Click on your domain/website to proceed to the next step
5. Click on "Virtual Dirs" tabs, then you can either click "Create Directory" to create new directory
or select existing Virtual Directory.
6. Fill in the directory name and select the folder.
8. Look for the Extension tab. Click on the "ASP.NET" drop box and select the version.
Remember to click "Update" and will be updated successfully.