Q: Can't delete Backup 3 files from computer

I have been using Backup 3 on my iMac for years, but it stopped working this week and now I'd like to delete all of my backups (I use Time Machine, so I don't need Backup anymore anyway).

All of my backups are stored on an external hard drive. When I select them, there is no option to delete. I have tried dragging them into the trash can and I get an error message that says, "The item “Computer Backups” can’t be moved to the Trash because it can’t be deleted."

How can I delete these files in order to free up space on my external hard drive?

Thanks!