how to increase size of drive c:

[Sediqi]

I have 3 drive, just I want one which should be c: only c:

 

[billy_2010]

Other two drives have important data?

Do you want to add the space from other two drives to C drive?

Windows 7 built-in Disk Management can extend and shrink volume, you can try to extend C drive.

 

[Isidore55]

Do you have multiple partitions on the same physical drive with C? If not, you have to buy a larger drive. But, if you do have several partitions on the drive and also has some free space there, you can try to add the free space to your C drive with the help of some free partition resizing tool: http://www.resize-c.com/
Of course, if the free space is continuously behind this C drive, you also can extend it in Disk Management directly.
PS: Do not forget to back up all important well before resizing your drive in case of data loss.