Modify records of several tables in an API 2

I have the following code, what I want is to modify the Student Name field, the Teacher Name field and the Class Name field

public IHttpActionResult CreateExamen(Alumno alumno, Maestro maestro, Clases clases)
{
    if (!ModelState.IsValid)
        return BadRequest();
    int promedio;
    db.Alumno.Add(alumno.Nombre);
    db.SaveChanges();
    return getAlumnos();
}

in the part (student.Name) I mark error because you can not convert a strin to the type ....