To access editing tools for your background (or any image) you can use the Transform menu. Click on the background and go to Frame on the top toolbar of the designer.
Then go down to Transform to access the functionality to flip an image, change the fit, opacity, and shape of an image box, or rotate 90 degrees at a time.
These items are also still available in their old locations in the Photo and Frame Settings tab located on the right hand side of the designer.
You can also crop the image inside the frame using the Crop / Edit button in the blue quick menu.