We are in the process of upgrading .NET framework version from 4.5 to 4.8 for a legacy application.

We have class library projects, web forms project and an ASP.NET MVC project.

1. The System.* assemblies for some of the projects in the the .csproj project file look as shown below. I don’t think these are installed as nuget packages; instead, I believe these are added as reference from the GAC. Is this assumption correct?

   If so, as part of the upgrade process, should I remove these assembly references and install them as nuget packages instead or shall I keep the assemblies as they are?

    <Reference Include="System" />
    <Reference Include="System.Data" />
    <Reference Include="System.Data.DataSetExtensions" />
    <Reference Include="System.Data.Linq">
        <RequiredTargetFramework>3.5</RequiredTargetFramework>
    </Reference>
    <Reference Include="System.Web.ApplicationServices" />
    <Reference Include="System.Web.DynamicData" />
    <Reference Include="System.Web.Entity" />
    <Reference Include="System.Drawing" />
    <Reference Include="System.Web" />
    <Reference Include="System.Web.Extensions" />
    <Reference Include="System.Xml" />
    <Reference Include="System.Configuration" />
    <Reference Include="System.Web.Services" />
    <Reference Include="System.EnterpriseServices" />
    <Reference Include="System.Web.Mobile" />
    <Reference Include="System.Xml.Linq" />
   

2. How do I determine should I need to use a newer version of the assemblies than the current ones while upgrading to .NET 4.8?

3. Here is the collective list of all the System.* assemblies that are referenced in the projects in the solution

    System
    System.Core
    System.Xml.Linq
    System.Data.DataSetExtensions
    System.Data
    System.Xml
    System.Configuration
    System.Data.Linq
    System.Web
    System.Web.ApplicationServices
    System.Web.DynamicData
    System.Web.Entity
    System.Drawing
    System.Web.Extensions
    System.Web.Services
    System.EnterpriseServices
    System.Web.Mobile