How do I completely remove windows 7 from a partition?

I've searched through google and haven't found an answer to this one. Today I finished building my computer and installed a fresh copy of Windows 7 Professional on it. I made a partition with only 15 GB of space and when I was on my desktop I realized it was too close to full capacity. So What I did was I went back into the BIOS, booted from the CD and restarted the whole installation process to where I could create/delete current partitions. So I basically deleted all the partitions I created before and figured it would solve the problem but it did not! When I deleted the C: partition I recreated another one with 20 GB of space (so there would be about 5 gigs of space after Windows was installed on it). What happened now is that it told me that at least 25 GB of space were required now to install Windows on it. The first time it only told me that about 9 GB of space were needed. That means that obviously the first installation of Windows was not deleted! I clicked on delete partition and I'm 100% sure I did it for all the partitions in the "Where do you want windows to install" window. Is there any way to permanently delete Windows 7 from my hard drive and re-try an installation that doesn't take up more space each time I try???? Thank you.