Any file manager from the market would do well. Go to directory /sdcard/clockworkmod/backup and you will see a bunch folders of the form year-month-date.ab.cd.ef where a b c d e and f are digits that I do not know what they stand for. Could be the time.
Those folders are the backups, with the date in the name being the date you made it. Delete the folders at will.
-Nkk