Deleted time machine backups from external HD, but did not free space Time machine backups filled my 4TB external HD.  To free space, I deleted a handful of the particular backups from:

/Volumes/Winston's 4TB/Backups.backupdb/  


Those files ended up in the trash bin and trying to "empty" the trash bin erred indicating the folder was in use.  So, I deleted the contents through terminal:

cd /Volumes/"Winston's 4TB"/.Trashes/
sudo rm -rf /501/2018-0*


Finder now shows the trash bin being empty, but the space has not been freed up on the drive.  How do I recover that space?
Enter Time Machine - there is an icon on the menu bar. Scroll back using the arrow keys on the screen until you get to the older backups. Near the top of the window, there is an icon that looks like a gear. Click on this icon and one of the options in the pull-down menu is to delete. Use this to delete backups.