The dismantle and mantle switch is a feature that every building has - but you have to understand that you can only use it on your tribe's buildings, never on enemy's.

 

When you place any plan, this feature is still inexistent, but after the first layer of the building  is constructed (1 wood pile), it will appear. To see the dismantle/mantle switch, just press mouse right click or keep your mouse on a building - either a damaged one, a building under construction, or a built one.

 

A building always have the mantle icon activated unless you click on it to switch to dismantle. Dismantle a building is sometimes needed, in order to replace it for a better one - or in order to get more braves by doing the dismantle trick. 

 

Take care not to accidentally press the mantle/dismantle switch, as the building will get dismantled against your will. This happens mostly on training buildings, because when units are being trained, the progress bar and the mantle/switch will show up, and players sometimes click on it when using the mouse to travel the camera. 

 

Obviously, only braves can dismantle a building, and if you switch to dismantle, the building will only get dismantled once a brave is sent to that building (unless braves were already in queue or inside that hut). Braves will carry wood to the front of the building's door, when dismantling it - this means that building has now less wood and is more vulnerable to atacks from troops and spells.