Hello indarv, welcome to Seven Forums!
To start, download and install the free Home Edition of the Partition Wizard program from the link below. Partition Wizard Free Home Edition
In the PW program, right click the "Free Space" to highlight/select it and click delete, that should make it unallocated space, you then may need to use PW to right click that new unallocated space and convert it from "Logical" to a Primary.
You should then be able to use Windows 7 disk management to extend the C: partition into that space; be sure to post back with any further questions you may have and to keep us informed.