You cannot simply "uninstall" .NET 4.0 because too many apps depend on it. Instead, follow this guide:
in machine.config:
The Microsoft .NET Framework 4.0, specifically version 4.0.30319, is a software framework designed to facilitate the creation of Windows-based applications. While it has been widely adopted and has played a crucial role in the development of numerous applications, it also has its share of vulnerabilities. These vulnerabilities can pose significant risks to systems and applications that rely on this framework. microsoft net framework 4.0 v 30319 vulnerabilities
The version string 4.0.30319 refers to the CLR build number. This same base version appears across Windows 7, Windows Server 2008 R2, and later OSes—but the vulnerability status depends entirely on the patch level (update rollup) applied to that build. You cannot simply "uninstall"
If migration is not immediately possible, organizations should implement strict compensating controls. This includes placing the legacy application behind a Web Application Firewall, employing strict input validation, and running the service with the least possible privileges. However, these are temporary stopgaps and do not solve the underlying security debt inherent in version 4.0.30319. These vulnerabilities can pose significant risks to systems