Speed walking/incline on a treadmill . TONE LEGS. need help?

so ive been running on da treadill for a month and my arms got toner, however my legs got reali musculr and thick. so i was wondering if i walked instead of ran , would that mke my legs skinnier? i heard my friend say tat walkin is better because it does not build muscles. becase muscle weight is hard to loose and looks buff.