Go down to “Themed Icons” and tap the toggle next to it. Now if you scroll back up, you’ll see a preview of how it’ll look with the icons on your current home screen.

With Nova Launcher and the icon pack of your choice installed, launch Nova launcher from the app drawer. The launcher will greet you with a setup screen. Scroll down and tap the check button to ...

However, it doesn't remove any apps from your phone, so you can start fresh and add the required apps on the home screen. With or without folders — that's up to you.