Properly delete and then restore everything in iCloud Photos
"Download and keep all originals" is the correct setting to get all your photos onto your Mac. These originals are stored in Photos Library.photoslibrary, you can check the exact location of your library by launching the photos app while pressing option.
You can also check for syncing problems by creating a smart album, looking for files failed to sync.

After you have double-checked all of the above and saved your library on a secure place you go to System Preferences -> iCloud and choose Manage in the lower right corner (I don't know the exact translation, I'm using my Mac in another language). In the popup menu, choose photos and then delete from iCloud Drive.

The photos will be stored online for the next 30 days, so you are able to download them again, in case you made a mistake. After that period (make yourself a calendar entry) you can activate iCloud Photo Library again, and all your files will be uploaded again.