How do I delete a building in the game?

To sell structures:

• Pick up a builder and hover him over the structure you want to sell.
• Two yellow circles will appear around the outside of the building.
• Hover over the circle with the bomb logo inside, (the other circle with the cross allows you to move the building).
• The circle around the outside will change colour from a blue outline to a thick yellow one and the middle will turn green.
• Drop the worker on the green section of the button
• The building will disappear leaving behind some debris and a small refund into your bank account.