Hi there,
There is no way currently to 'take a backup' of your iCloud storage. You'll have to drag and drop stuff onto your desktop manually. To answer your question on how to remove the storage, on your iPhone:
- Go into Settings.
- Tap your name at the top of the screen. This will show your iCloud details.
- Tap the iCloud tab, below Subscriptions.
- Tap Manage Storage.
- Scroll down and tap iCloud Drive. This will show you what things you have in your iCloud Drive at the moment.
- Tap Delete Documents & Data.
I hope these answers help you solve your issues you are currently having.
Grey360