I'm not sure I completely understand the question.. if you are wanting to destroy your own city, to start again elsewhere, you have a 'Restart' option, found in the 'Settings' menu. That will cause your current city to be abandoned, and you will start again with nothing, on the rim of the world. This will destroy all cities that you own, not just the currently selected one.
If you mean to destroy someone else's city.. that isn't really possible. The only way for a city to completely be destroyed, and disappear leaving space for another, is for the owner to restart causing it to ghost. The city will then degrade over time until eventually it disappears.