The form submission notifications that send by default when one of your forms is submitted are not customizable. These notifications include basic information about the form and properties that the contact filled out.
If you're using the workflows tool in a Marketing Professional or Enterprise account, then you can create custom internal notifications. Check out this article to learn how to create custom form submission notifications. Please note that if you're using workflows in a Sales Professional account without a Marketing Professional or Enterprise subscription, you will not be able to set up custom internal notification emails.