How do I delete all the discovered computers unmanaged

I have over 5000 devices discovered unmanaged I want to delete all 5000 of them and then go into the discover computer tab and put in IP Ranges. Is that possible and if so how do I do that. And that's all I would ever want to show up in the discovery view is though's IP ranges that I have specified and then you just have to push the agent out to them. Thanks for any help.