1)  Go to "Extensions" -> Choose Modules

2) Next, at the modules -> click Search Tools button -> select type popupContent

Go inside the module by click on the title

3)  Go to "Full Width Content" tab and start edit the content

4) If want edit the image just choose the image and click delete

5) Then choose new image from your device and drag into the place

6) After new image successfully change, click button "Save" at the top once you have done

7)  If you want to unpublished this feature, just untick the status -> "Unpublished"