It is possible to select an ASP.NET version based on the code generated for the website.
For ASP.NET 2.0–3.5, select version 3.5, and for ASP.NET 4.0 and higher, select version 4.5.
ASP.NET can be set in Plesk in two ways:

• From Hosting Settings
• From ASP.NET Settings

Here are the steps to set the ASP.NET version in Plesk from Hosting Settings:

1. Enter your login credentials to access the Plesk control panel.

1. On the dashboard, select Websites & Domains.

1. Select Hosting Settings from the menu.

1. Select the Microsoft ASP.NET support version from the drop-down box in the Web scripting and Statistics section. After selecting the required version, click OK.

Here are the steps to set the ASP.NET version in Plesk from ASP.NET Settings:

1. The first step is to log in to the Plesk control panel by entering your login credentials.

2. On the dashboard's left side, click Websites & Domains.
   

3. Select ASP.NET Settings from the menu.

1. Click on Change Version.

1. From the Selecting the ASP.NET Version window select the version you need and click OK.

And, that's done!
In this manner, you have successfully set up the ASP.NET version for a website in Plesk.