Google's just unwrapped more three-dimensional buildings in a number of cities worldwide, including London, Paris, Barcelona, Stockholm, Singapore, Lisbon, Boulder (Colo.) and 11 cities in South Africa. Those are in addition to New York City, Zurich, Milan and others.
You don't have to do anything -- the updated maps are all on Google's side. To view the 3D buildings, just make sure you're viewing things in map mode (not satellite), then zoom in and use two fingers to change the viewing angle.
And in case you're wondering, the image above is from the site of Mobile World Congress in Barcelona.