Can I replace the default image for System Pages?

The image used on the 404 and 500 Error Pages can be replaced in Theme Settings

Change image on 404 and 500 Error pages

From Theme Settings, click System Pages:


Expand the Error 404 settings and change the dropdown to Custom Image:


Use the file selector to Upload or Browse images and select the image you want to use.

If you don't want an image, there is also the option for No Image.

The same option is available for the Error 500 system page:


If you previously created a custom template for the 404 or 500 error pages in your child theme and the only change you made was to the image, you can use the theme settings to upload your image and then remove the custom template from the child theme to revert back to the default template.