just got new imac with fresh Mavericks install, old data still remaining, how to find and delete?
You do not need a disk to reinstall Mavericks, since it has a recovery partition that will download Mavericks and do a fresh install, if you prefer to do that.

Erase and reinstall Mavericks: http://support.apple.com/kb/PH14243

Otherwise, you can probably just delete the user account, which will offer to delete all the user's info, freeing up considerable space.