|What you are talking about is re-sizing partitions.|
You have not given any details on the size of the partitions you currently have.
Before considering using partitioning tools you need to know there are real risks associated with such an undertaking. If anything goes wrong (and it often does) you could lose all.
There may be alternative strategies you can use to free up space on your C drive such as moving your "My Documents" folder from C to D as well as uninstalling games & Programs from C and re-installing them to your D drive.
You can also limit the size of your recyclebin and System Restore folders to free up further space.
Goin' Fishin' (Some day)