Album Artwork

I like to change my album art for my songs but all songs for one artist that I have, the album covers have changed to the same one. The only thing that works is if I remove the artist name or add an album name but they are all singles. I didnt have this problem before I got the songs but all of a sudden when I was going through them to change the album art to a higher quality every time I pressed OK it just changes to the same album cover of another song