How to quit Karate? Please Help?

Okay, So I have been doing karate for about 5 years now (I'm 14) And I have slowly been losing my excitement for it.(I am a second degree brown belt.) I am staring to want to learn t play guitar and my mom said I have to choose between Guitar lessons or Karate. I want to quit but I don't want to hurt my sensi feelings or anything. (and I am kinda afraid I might cry because I am kinda emotional) I want to try someting else I think I need to take a break for karate and see if it's what I really want to do. Do you have any sugestions on what I can tell my Sensi about quiting. I don't want to be all like i'm quiting because I want to do guitar. Oh and also I am a very shy person so it will be awkard.Thanks :)