How can I delete all my photo’s from iCloud?

Adding to gail's excellent suggestion, open Photos, go to Photos/Preferences/iCloud and set up syncing. Then go to System Preferences/iCloud, sign in, and check Photos syncing. Once all the Photos have synced to your computer, quit Photos. You should now have a complete compilation of your photos (like a Master Library). Reopen Photos with the option/alt key held down and create a new system Library. You can now delete photos from your devices while maintaining a master copy on the computer. Turn off iCloud syncing when reverting to the Master Library.

Photos - Use multiple libraries in Photos

The easiest way would be to make sure they are backed up to a safe place (like a separate Photos Library, or on a Time Machine backup, and then deleted them from iCloud via your Mac or iOS device.

Again, the photos need to be safely stored away, then turn on iCloud Photo Library on the Mac, and under the All Photos album, select all, then delete them.

Trying to delete large amounts of photos from iCloud.com tedious and not conducive to getting it done quickly.

Best of luck,

GB