Music Hacking FFV on FF6

Hey this is my first post in this forum and i have a problem about music. I would use music of FFV in FF6, not all the playlist just one or two music about FFV but i want change the Boss battle song, The Fierce Battle about Atma Weapon and the Final Battle just that. I don't understand how to change the Music if someone can explain me better i think can could help me. Thanks for you understand !  

PS : I have already read the FAQ and some subject about "How to change music" like me but no one help me about my change 
PS2 : I have a Hex Editor and all stuff about to change music