Update system requirements

Author: nade7o

installation-and-upgrades/system-requirements.md

@@ -25,7 +25,7 @@ Telerik UI for WinForms can be installed on any operating system that supports .
 ## .NET Framework and .NET  
 
 - [.NET Framework 4.6.2, .NET Framework 4.8 and later](https://learn.microsoft.com/en-us/dotnet/framework/get-started/system-requirements) 
-- [.NET 6, .NET 8, .NET 9 and later](https://github.com/dotnet/core/blob/main/os-lifecycle-policy.md) 
+- [.NET 8, .NET 9 and later](https://github.com/dotnet/core/blob/main/os-lifecycle-policy.md) 
 
 ## Development Environment