In order to delete old backup file You can try to use this:

DECLARE @TrnBckFileToDelete as varchar(255)

DECLARE ExpiredTranLog_CURSOR CURSOR FOR

    SELECT msdb..backupmediafamily.physical_device_name

    FROM   msdb..backupset INNER JOIN msdb..backupmediafamily

    ON     msdb..backupset.media_set_id = msdb..backupmediafamily.media_set_id

    WHERE  msdb..backupset.expiration_date...