If you are looking for a way to clear out the system data on mac, start by going through System Settings > General > Storage. Look at the big files, the downloads, the apps and the backups and delete all the data that you don't need anymore. Don't forget to empty the Trash after the process. In case you use your iPhone or iPad along with your Mac, see if the local backups from them occupy storage space. You may even consider restarting your Mac since some of the temporary files will be removed during that process.