I want to start running 3 days a week?

I live in a hilly area in new england too! AND I have big butt and thighs LOL. Here's what I do, I go to the gym. Walk 5 minutes, run 2 minutes, walk 5, run 2...keep doing that until you've reached the distance you're aiming for. You can build it up too, walk 3, run 3 etc. This will SLIM your legs, not bulken them.