How to update parent form when changes made to the child form.

label1;

            public string LabelValue
            {
                  get
                  {
                        return this.label1.Text;
                  }
                  set
                  {
                        .label1.Text= value;
                  }
            }
      }

then from the child form:

if (this.Owner is ParentForm)
{
      ((ParentForm)this.Owner).LabelValue = @"Some label value";
}

when you show the child form, you pass the ParentForm as the owner.