Deleting Time Machine BackUp files from Internal Raid Storage

I have just discovered that Time Machine has filled up my Raid Storage drive. Obviously I tried to delete the folders from the 'Backups.backupdb', folder selected as the TM destination. But as you most probably know, this doesn't work and just wastes your time without explanation of why trashing TM backup folders won't work. (error code - 8072).

I have also read that formatting the disc is another solution to clearing the TM files, this however does not help with the clearing of select unneeded files in TM so as to leave the media being used in current projects.

Does anyone know how I can delete all my TM backups, apart from the perhaps the 2 most recent backups....I only need a couple of successful backups to feel secure and safe, not 8 months worth of the same stuff which has just clogged up my storage drive?

Opie