Setting two different list for combo box with the radio button selecti

In my asp.MVC application I have created two combo boxes as Manager and TopManager. I have loaded Manager list to the Temp list and another Temp list to the Top managers list.

@using Asp_PASMVC.Infrastructure
@{
    List Employees = (List)TempData.Peek("EmployeeList");
    List TopEmp = (List)TempData.Peek("TopEmpDroDown");
    if (Employees.Exists(x => x.Value == "1"))
    {
        Employees.Where(x => x.Value == "1").First().Selected = true;

    }
    if (TopEmp.Exists(x=> x.Value =="1"))
    {
        TopEmp.Where(x => x.Value == "1").First().Selected = true;
    }
    string UserLvel = TempData.Peek("UserLevelClaims").ToString();

}

Here is the View 

    @using (Html.BeginCollectionItem("ApprovalPartyList"))
    {
        

            

                

                    For Manager
                    

                        @Html.RadioButtonFor(m => m.Approve_Type, false)
                    
                
            
            @if (UserLvel != "1")
            {
                

                    

                        For Top Manager
                        

                            @Html.RadioButtonFor(m => m.Approve_Type, true)
                        
                    

                
            }
        
        

        

            

                

                    Select the Approver
                    

                        @Html.DropDownListFor(model => model.Approver_Id, Employees, new { @class = "js-dropdown" })
                        @Html.ValidationMessageFor(model => model.Approver_Id, "", new { @class = "text-danger" })
                    
                
            
        
        Delete
    }

The issue is combo box only shows the Manager list ( I have assigned ) , I want it to change If Radio button ` Manager ` selected the combo box should load the 'Employees' and If 'Top Manager' Selected, Should load the 'TopEmp' list to the combo box. I think this shold be done with javascript. But no idea of creating that. Can you help me on this ? Thanks in advance.