Factory default installed the Win7 in C drive (occupied 90% of the total hard disk space) without partition. How can I create a separate partition with reformat C ?

I got 3 partitions too but beside C, the other 2 partitions are very small size meant for recovery only. I was wondering how we can create a sizable new partitions out of C drive for storing important personal data like photos, work, assignments ? In the even of OS failure, we can just reformat C drive.