Kimsan,
Where did you upload the files to? Media library or in the content tree?
As of right now I don't know of any tool or program out of the box but I believe Bizstream has created a pretty nice search tool that's part of their Compare for Kentico solution. I'd give that a look. Some solutions I can think of though would be:
- if the assets are in the content tree, when you delete them you can automatically forward them to a different page. This means you'd be deleting blindly and not the best thing.
- create some custom module or code that would take the files from the media library or the content tree and scrap the site to look for that relative URL.