I don't know for sure, but here is what I assume: You are looking on the media card at files the app created when you installed it. There may even be a specific folder the app created that contains the files. You have now deleted the app but the files remain, you think. I'll assume you are correct that the files belong to the app that was deleted and were left after the app was deleted.
If all the above is correct, you probably won't do any harm deleting the files. However, the best practic is to do a full backup before you do anything like this. Don't mess around. Do the backup. Then if it turned out to be the wrong thing to do deleting the files, you can restore from backup and be back in business. Worst case, you will have to reload the OS, too, but you will have your data to restore afterward.
Last edited by aiharkness; 10-05-2012 at 07:16 AM..