MUSCLES:: How can I let go of my muscle? I am a girl.?

I am 15, a girl, caucasian and natually very muscular. I have bulked upper body muscles, like my arms and my shoulders muscles. How can I not look som much like Buzz Lightyear? I have gone before for 3 motnhs without using my arms for hardly anything and I was still very strong and muscular. Please tell me how I can just not look so BULKED?