How to maximaized window form

Actually, just thinking some more about this, how are you going to click a button on a minimized form?

Do you mean to maximize a different form, say Form2?

Form2 form2 = (Form2)Application.OpenForms["Form2"]; // unless you already have a reference to Form2

Try:

if (this.WindowState == FormWindowState.Minimized)
{
    this.WindowState = FormWindowState.Maximized;
}