I would like to update my character sheet background without first deleting the whole sheet. Can I do it?
Yes you can.
Enter Build Character mode, then click on Pages in the top right corner. When you move over the page you get two options: Replace and Delete.
Choosing Replace allows you to replace the image without moving or removing the Stats.
If you Replace with a multi-page PDF, the page you replaced and any following pages up to the number of pages in your PDF will be replaced and added, up to a maximum of 10 pages.
// Closing as Resolved