Can I overwrite the previous backups rather than add other ones to the target directory?

SQLBackupAndFTP doesn’t have the option to overwrite the previous backups but it can delete backups automatically after a certain period of time. Using “Auto-delete” option you can achieve the same result as if you overwrite the previous backups.

To tune this option go to the “Store backups in selected destinations” section, select a place where your backups will be stored and specify the time interval, after which backups should be deleted at the “Auto delete after” box.