SC2Mapster

Hi, I need guidance on how could I remove an armed magazine when I arm another weapon. To clarify: Currently the ghost academy can build the standard nuke. But I've added another ability to the ghost academy where you could upgrade the nuke once the standard nuke has finished building. I would like the standard nuke to be "removed" once the "upgraded nuke" has finished construction. Where or how could I achieve this? Any help is greatly appreciated. Thanks in advance.