Most pages share the same method for updating background images, but team pages and post pages are handled differently through the CMS.
Most pages
Navigate to the page you want to update and click Back to editor.
Find and click the collection item on the page.
Click on the background image field and select a new image.
Exit, click Preview, and refresh the browser to see the updated image.
Team pages
Team pages are found under Groups. Their background image is not set on the page itself — it is managed centrally.
Go to CMS → Business Data → Business Images.
Find the team page background image field and replace it with your new image.
The update will apply across all team pages.
Post pages
Post pages are found via Groups → Post. Like team pages, their background is managed in the CMS.
Go to CMS → Business Data → Business Images.
Find the field labelled Post Page Background and replace the image.
The update will apply across all post pages.