Best Methods for Losing Mass in the Upperbody for an MtF Transgender?

I am 6'2" currently weighing 255#. I have been on a feminizing hrt regimen since May 2012. I am working out using cardio exercises as my main source of activity including yoga(for beginners). I don't really care about weight exactly but more of shape and size. What are the best methods for losing mass for the upperbody for someone who gains muscle mass quickly when working out with weights.

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