You can demolish some buildings but you will lose Power points, as well as the bonuses that these buildings provided.

To do so, select a building and tap the "Demolish" button in the window that appears. You will see the Demolition window where you can choose how to conduct the demolition.

To destroy a building instantly, you need the Demolition item. You can purchase this in the Item Store.

You can also dismantle a building for free but this will take half the time that was spent to upgrade this building to its current level.

Note: if you demolish a building, the resources you have spent on its construction will not be returned.