public class Person {
    [XmlElement]
    public int Id { get; set; }
    [XmlElement]
    public string Name { get; set; }
}
//=========
XmlSerializer formatter = new XmlSerializer(typeof(List<Person>));

        List<Person> personList = new List<Person>();
        personList.Add(new Person { Id = 5, Name = "Bob" });
        personList.Add(new Person { Id = 15, Name = "Tom" });
        Person kate = new Person { Id = 115, Name = "Kate" };
        personList.Add(kate);

        string filePath = @"C:DELEteME.xml";

        using (FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate)) {
            formatter.Serialize(fs, personList);
        }

<?xml version="1.0"?>
<ArrayOfPerson xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Person>
    <Id>5</Id>
    <Name>Bob</Name>
  </Person>
  <Person>
    <Id>15</Id>
    <Name>Tom</Name>
  </Person>
  <Person>
    <Id>115</Id>
    <Name>Kate</Name>
  </Person>
</ArrayOfPerson>

personList.Remove(kate);
        using (FileStream fs = new FileStream(filePath, FileMode.OpenOrCreate)) {
            formatter.Serialize(fs, personList);
        }

<?xml version="1.0"?>
<ArrayOfPerson xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Person>
    <Id>5</Id>
    <Name>Bob</Name>
  </Person>
  <Person>
    <Id>15</Id>
    <Name>Tom</Name>
  </Person>
</ArrayOfPerson><Id>115</Id>
    <Name>Kate</Name>
  </Person>
</ArrayOfPerson>