What use instead Entry?
var person = Persons.Where(p => p.Age == 12).FirstOrDefault();
Entry(person).State = EntityState.Modified;
person.Name = "Josh";
SubmitChanges();
And i have error : CS0103 The name 'Entry' does not exist in the current context
Comments
(Entry(person)).State = EntityState.Modified;
This will work, assuming 'Entry' exists. (Entry is not part of LINQ to SQL, are you using Entity Framework or something else?)