You can change your form's Title or Description by clicking on the Title or by clicking the Form Settings button in the bottom bar on the Build page. This will bring the land-hand Form Settings panel back into view.
The Title is what the form will be called, and this will also appear at the top of the form.
Warning: Your form's title is used as part of the URL for your form's public web address. If you have already advertised your form's link and the change the title, you will need to make sure that your form's link is updated anywhere it is advertised. You can copy your form's new URL from your form's Publish settings.
The Description will appear at the top of your form underneath the Title, and can give the user a brief description of what the overall form will be about.