Don't think there is a default tool in mendix for this. There is a workaround:
- Add new image to your image collection
- Copy the name of the old image
- Delete the old image
- Give the new image the same name as the old image.
Alternatively, if your looking to batch replace CSS class names then this is a great script to do just that:
https://github.com/JelteMX/mendix-project-class-renamer
Using the Model SDK it can batch change class names in your application.
Regards
Simon