Loading Master Page Dynamically

Add a master page in your solution explorer and named it as "MasterPage.master" 
Paste the following code in between div tag 

<table width="100%">
            <tr>
                <td style="background-color: Red; color: White; height: 70px; width: 700px; font-size: x-large"
                    align="center">
                    Master Page1
                </td>
                <td style="background-color: Aqua; color: Black; height: 70px" align="center">
                    <asp:LinkButton ID="LinkButton1" ForeColor="Black" runat="server" OnClick="LinkButton1_Click">Master Page 1</asp:LinkButton>
                 
                    <asp:LinkButton ID="LinkButton2" ForeColor="Black" runat="server" OnClick="LinkButton2_Click">Master Page 2</asp:LinkButton>
                </td>
            </tr>
            <tr>
                <td colspan="2" style="background-color: ButtonFace; height: 300px">
                    <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
                    </asp:ContentPlaceHolder>
                </td>
            </tr>
        </table>

Add one more master page in your solution explorer and named it as "MasterPage2.master"
Paste the following code in between div tag 

<div>
        <table width="100%">
            <tr>
                <td style="background-color: Lime; color: Black; height: 70px; width: 700px; font-size: x-large"
                    align="center">
                    Master Page2
                </td>
                <td style="background-color: Red; color: White; height: 70px" align="center">
                    <asp:LinkButton ForeColor="White" ID="LinkButton1" runat="server" OnClick="LinkButton1_Click">Master Page 1</asp:LinkButton>
                   
                    <asp:LinkButton ForeColor="White" ID="LinkButton2" runat="server" OnClick="LinkButton2_Click">Master Page 2</asp:LinkButton>
                </td>
            </tr>
            <tr>
                <td colspan="2" style="background-color: ButtonFace; height: 300px">
                    <asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
                    </asp:ContentPlaceHolder>
                </td>
            </tr>
        </table>
    </div>

Paste the following code in MasterPage.master.cs and MasterPage2.master.cs files 

protected void LinkButton1_Click(object sender, EventArgs e)
    {
        Response.Redirect("Default.aspx?master=First");

    }
protected void LinkButton2_Click(object sender, EventArgs e)
    {
        Response.Redirect("Default.aspx?master=Second");
    }

Add a new Web Form and named it as "Default.aspx" and set its default master page,that is "MasterPage.master"

<%@ Page Title="" Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

Paste the following code in _Default class in Default.aspx.cs file

protected void Page_PreInit(object sender, EventArgs e)
    {
        if (Request["master"] != null)
        {
            switch (Request["master"].ToString())
            {
                case "First":
                    Page.MasterPageFile = "MasterPage.master";
                    break;
                case "Second":
                    Page.MasterPageFile = "MasterPage2.master";
                    break;
            }
        }
    }