Definition of "converted"

Think of banking today and the image is of grey-suited men in towering skyscrapers. Its future, however, is being shaped in converted warehouses and funky offices in San Francisco, New York and London, where bright young things in jeans and T-shirts huddle around laptops, sipping lattes or munching on free food.

2013 August 3, “Revenge of the nerds”, in The Economist, volume 408, number 8847