Editing Related List/hover fields is quite simple. The hover fields on an object page, are the same fields in your Related List at the bottom of the page. In this example, we'll use the Project hover fields from the Prospect page.
Note: Only the System Administrator User at each company will be able to make these changes.
See also: System Administrator Training
You'll navigate to Setup > Create > Objects > Prospect (or other object) > Page Layout. Scroll down to the Project related list and select the wrench icon:
Make your changes and Save. Run First Time Setup!
Watch this video and follow along in your system: