Replacing Characters in String Using C#

using System;
public class Program
{
public static void Main()
{
      string strFirst;
      char chrOld;
      char chrNew;
      Console.Write("Enter Your String:");
      strFirst= Console.ReadLine();
      Console.Write("Enter Old Character:");
      chrOld= Convert.ToChar(Console.ReadLine());
      Console.Write("Enter New Character:");
      chrNew= Convert.ToChar(Console.ReadLine());
      Console.Write("Your Replaced String:");
      foreach(char chr in strFirst)
      {
         if(chr==chrOld)
         {
            Console.Write(chrNew);
         }
         else
         {
            Console.Write(chr);
         }
      }
   }
}