Hacked

Can someone tell me how to remove files that were put on my system by a warez hacker using my server as an ftp for his pirated software. I was able to remove of the files but some wouldnt let me delete them. Does anyone know how to remove this files. (they’re mostly .mp3, .exe, .avi file extension but when I go to delete them it gives me an error that they couldnt be deleted for some odd reason.)