Photo Library on Mac

If you open the Photos app, press CMD key and the comma key this will open the Preferences window. If you click on the General icon it will give you the path to where your library is stored on the laptop.

However, rather than delete the entire library, if you click on the iCloud icon in the Preferences window you can select 'Optimise storage' rather than Download originals. This will allow you to still view your photos on your laptop but will reduce the space used by the library.

You can simply delete the library using Finder as you would any other file or folder. The library containing your photos is separate from the Photos application. Obviously you will lose all of your photos - presumably you have them backed up in multiple places elsewhere?

You're welcome.

I would strongly recommend that you keep a full back up of your photos somewhere. iCloud Photos should only be thought of as a syncing service not a backup service. There have been a few instances on this forum where a problem has arisen and photos have been deleted on one device which is then instantly synced across all devices and the individual has not been able to recover their photos. Even if you maintain a local backup of your iPhone data this will not include your photos if you have iCloud Photos switched on.