How do I adjust the background picture size to show full picture?

If you are referring to the page background image of the only form in your account, I suggest you add the following CSS codes below to your form. To learn how to do that, please see this guide: How-to-Inject-Custom-CSS-Codes

.supernova {

    background-size: 100% 100% !important;

}

I hope this helps. If you have any further questions or concerns, please feel free to contact us again anytime.

Thank you.