Contact Form Field Validation

Hi I have this contact form installed on my server (uploadead files). The for works fine but I need the form to validate all the marked fields. The form has many fields so if some of the top fields are missing I am not going to be able to see them ... so I would like a message to appear at the top of the submit button the fields that need to be filled correctly. Also validate that the email must have the @. I hope I explained myself. Thanks.