How can I change the background image of the form?

Q2. I was able upload a picture that comes up with the link when I post the form. I forgot where I went to add the picture. Can you help?

Are you perhaps referring to your form's background image? If so, click the blue FORM DESIGNER icon on the right > go to the CUSTOM tab > then click REMOVE IMAGE. Afterwards, upload a new one if you wish to change it.