You'd have to really change the function and then the template to do so. At first glance it doesn't seem very easy if you are new to coding.
Here is where the button and URL are created:
Then in the template the button is displayed within the tile:
https://github.com/dbnschools/moodle-theme_fordson/blob/master/templates/fpmarkettiles.mustache
This will break the multi-functionality of the marketing tiles to do both text and photos. You'd also have to maintain any changes moving forward with each upgrade.