Save space by storing your content in iCloud or using built-in tools to find and remove large or unneeded files.

Optimized Storage can help you save space in iCloud and making it available on demand instead of having it stored locally all the time on your device. When storage space is needed, things that you seldom use will be stored in iCloud by default. Files that you accessed recently, will stay on your Mac.

Choose Apple menu > About this Mac > General, then click Storage. Each segment of the bar is an estimate of the storage space in use by a specific category of files. You can point your cursor at each section to get more details about it.

Click the ⓘ button to expand the section you are wanting to manage.

Click the Optimize Button, then choose from these options:

• Automatically remove watched movies and TV Shows. This will perform the specified actions to keep your storage use lean.
• Download only recent attachments. Mail will only automatically download the attachments that you recently received.
• Don't automatically download attachments. Mail downloads an attachment only when you open the email or attachment, or save the attachment to your Mac.
  

Empty Trash Automatically.

This will automatically permanently delete files that have been in the Trash for more than 30 Days.

Reduce Clutter

This helps you identify large files and files you might no longer need. Click the Review Files button, then choose any of the file categories in the sidebar, such as Applications, Documents, Music Creation, or Trash.

You can delete the files in some categories directly from this window.  Other categories show the total storage space used by the files in each  app. You can then open the app and decide whether to delete files from  within it.

How to free up storage space manually

Even without using these Optimized Storage features, you can take other steps to make more storage space available:

• Music, movies, and other media can use a lot of storage space. Learn how to delete music, movies, and TV shows from your device.
• Delete other files that you no longer need by moving them to the  Trash, then emptying the Trash. The Downloads folder is good place to  look for files that you might no longer need.
• Move files to an external storage device.
• Compress files.
• Delete unneeded email: In the Mail app, choose Mailbox > Erase  Junk Mail. If you no longer need the email in your Trash mailbox, choose  Mailbox > Erase Deleted Items.

For the most up to date info, please see this website: https://support.apple.com/en-mide/HT206996