Weights and a confusion

Hello everyone.

Hope you all are having fun working out. I was just thinking...if I lift heavy with fewer reps...I gain muscle and with lighter weight s and more reps...I tone my muscles right???

If that's right,then I have a confusion. I am 155 lbs and 164 cm is my height. I am more heavier in my upper body and I look bulkier than I am..for my height. I tend to easily gain weight on my chest,shoulders ,upper back and I have heavy arms.... I want to tone and shape my upper body.

I am infact thinking of buying fb flex . But I am confused about lifting weights. I don't want to add muscle to my already heavy upper torso.

What is the scince behind this ? Guys plz help

I have another doubt.... Kelli and Daniel lift so heavy...still they are not muscular ...