Slitherine

I need to be able to scrap a building in order to make room for a different one. I tried high lighting the one I want to scrap and then touched the "scrap" button. However nothing happens. I am sure I have missed some simple step but I cannot find it in the manual.

What do I need to do to make this work?

Thanks.

OK I sorted it out. It has to be done in the reverse order.