1) Go to SP Page Builder -> Choose "Pages"

2) Next, choose the Home page you would like to edit. Then click on the title to edit

3. Then you go to SlideShow at first row -> Next click pencil icon to start edit the addon

4. Go to settings icon to edit the slideshow content

5) Scroll down the style, you will see the the background image. Choose the image button to upload the new one

6) Upload the image file from your computer, then click insert 

7) After upload the image, click the button 'Apply' on the bottom

8) Last, save the page by click the 'Save' button on the right top