How can i reduce the size of my calves?

I will presume that you are relatively fit and not overweight as you said muscular. You can reduce a muscle by reducing the stress it is put under. If you walk predominantly on the ball of your foot (toe end) this will cause a greater strain on your calves increasing muscle. You could try walking more with the heel and pulling with your leg. Don’t wear high heels often as they cause strain = muscle growth. Try performing cardio, something long distance like a marathon will cause your muscle to waste away/ change fibre composition. Certain sports will increase calve size e.g. horse ridding, hill walking and sprinting etc.