I have an External 1 TB HDD where 250 GB of it is dedicated to Time Machine back-ups. I only have about 25 GB of space left but Time Machine won't update .. says there's not enough space. I thought that TM auto-deletes the oldest entry? Well it's not working. What should I do? Do I need to do into Disk Utility and just highlight my TM Partition and erase it then start over? There's nothing on it that I need.