For change homepage section(s) background Image,
Please Follow below given steps :
- Please login to your wp-admin
- Click on customizer under appearance.
- Click on Theme options settings.
- Click on Custom Header Settings.
- you will see images change option(s) like below given.
Then Please click on save and publish button for get changes live.
If you don't see options like this , please ask to support team for theme update.