How'd You Get them Guns?!

I'm training for a 10k (running and toning several days a week) and working out with a personal trainer, and while I know you can't spot train/choose where weight comes off, I have SUCH envy of people with sculpted arms! Right now, mine are huge and embarrassing. They are quite muscular, and I've grown stronger in my ability to do pushups, planks, weights, etc, but they have layers and layers of fat on top so they just look and feel disgusting.

For a while I felt like having lean, sculpted arms was an impossibility, but seeing some of your success stories, I'm inspired and believe it's possible! What I want to know is, when in your fitness journey did you see the transformation happen most? Was it gradual over time? Were there specific changes you made to diet or exercise that you think helped more?