Commerce - Theme Add-to-Cart form on Product Display page
Here's a good start on your first form alter for add to cart:

function MODULENAME_form_alter(&amp;$form, &amp;$form_state, $form_id){
  // Add to cart form overrides
  if(substr($form_id, 0, 30) == 'commerce_cart_add_to_cart_form'){
    kpr($form);
  }
}