Upload your desired backgrounds into your event via the Event Manager website. You can do so by opening your desired Event, selecting Extras, then Graphics, then check Enable Background Removal. You'll see a box appear allowing you to browse through images to include from your computer. After your selection, be sure to save your event and refresh the PPU Helper for the changes to take effect.
Navigate to the Green Screen tab of Photo Booth Upload Settings.
Find and click the box in the upper right corner that says Save Original Photo to Output Folder:
Select a green screen and take some photos!
On the PPU Kiosk, open Settings and navigate to the Photo Edit tab.
Make sure Photo edit is not disabled, and select Chroma Key in the Background Removal section:
Click the Settings button to adjust your Chroma Key color, threshold, and softness. Click OK twice to save your settings.
Find your original image in Slide view and click Choose Background. You'll now have the option to choose the backgrounds you uploaded in your event, and position the image in that background.
When you're satisfied with the look of your image, lick Done Editing at the top to save it. Press Select under the new image and share it normally.