Many Mac owners use Time Machine to backup your files, documents and settings on an external drive. Over time, however, the free space becomes less. The best way to free up space on an external drive — delete old Time Machine backups.
By default, Time Machine deletes old backups as the disk is full. To get rid of all the backups created in a certain period of time, follow the instructions.
1. Click on the desktop and open a new window by selecting “New Finder window” from the file menu or using the shortcut Command + N.
2. Connect the drive with the backups to the computer and wait until it will appear in the “Devices” section in the sidebar of Finder. You may be prompted to enter the name and password of an administrator for further action. If you’re using an AirPort Time Capsule, you need to specify the password to access the backup drive.
3. Navigate to the folder “Backups.backupdb” Time Machine.
4. Locate the folder with the computer name. For example, if your computer is called iMac Retina, Time Machine will store the backups in the folder “Retina iMac”.
5. Inside you will see many folders whose names indicate the date of their creation. To delete a backup, click the right mouse button, then “move to trash”.
6. Repeat this process with all the backups that you plan to remove. Then disconnect the disk by selecting its icon on the desktop, and then click “Eject” in the Finder menu.
You can only delete folders “Backups.backupdb”, remove individual items in the subfolders with the dates is not permitted.