In Windows 7 you can go to Disk Management in Computer Management to expand a partition.
Press the Start key or open Windows Start menu.
Right-click "Computer", choose "Manage", then go to Disk Management at Storage and right-click on a partition to "Extend Volume".
It is better to post a screenshot of the disk management, so that we could know your disk configuration. To expand C there are several software could do this AOMEI Partition Assistant Home (freeware), EaseUS, Paragon,Gparted(open source). In these software AOMEI is much more flexible, it provide one-click solution directly allocate free space to C drive, you can learn more from this review: http://www.pcworld.com/downloads/file/fid,222251-order,...