You can just turn off background music in the options either in game or with the launcher.
I strongly just recommend doing this..
But, if you really insist of deleting that file, just go to:
C:\Program Files\Epic Perfect World\element\music
The opening theme is theme a, I believe. However, I haven't done this myself, so I can't guarantee the result. The launcher might even automatically fix the file, I'm not sure. Agatio would be the one to ask about that.
Good luck!