With Bulldozer a selected building or an area can be destroyed. Instead of this tool you can press Delete. A building that was built as a result of zoning will be destroyed, but not the zone when Del is pressed. Depending on the need a new building can rise. It is recommended to destroy a bankrupt building. There is also a circular bulldozer thread that can delete up to 9 small zones and a road at the same time. The circular bulldozer can be adjusted in size from about 60x60 (.5) to about 400x400 meters, by right clicking it and using the slider.