Use the hover option in any Divi module to change the image hover.

Source: http://www.elegantthemes.com/blog/divi-resources/how-to-create-a-rollover-image-effect-with-html-divi-nation-short

This can also be done with HTML.

Paste this in the Divi code module (or the WordPress text and never switch back to the visual editor).

Then replace the IMAGE1 and IMAGE2 with the images (full path from the media library).

< img src="IMAGE1" onmouseover="this.src='IMAGE2'"
onmouseout="this.src='IMAGE1'" />Code language: HTML, XML (xml)