When I installed Windows with Boot Camp, I only allocated about 32GB for the C: drive. Unfortunately, it didn’t take long to run out of space even though I don’t use it much. Turning off hibernation freed up space, but not enough to resolve the problem. The next step was to re-size the partition, which is slightly harder than it sounds.
Reduce Size of Mac Partition
Open Disk Utility, and select the top level of the internal SSD/HDD. Then click Partition at the top. Select your Macintosh HD partition, then under Partition Information > Size, reduce the size of the partition. Note that you are limited by how much space is already used (this amount is listed just below the Size text field). Click Apply.
Increase Size of Boot Camp Partition
If resizing Macintosh HD is successful, your next step is to boot into Windows. Open the Start menu, then type Disk Management. Look for your C: drive. Disk Management will only allow you to extend the C: partition if the free space you just created is to the right of it. If it is listed to the left, you must use a free 3rd party utility like MiniTool Partition Wizard Free. Here’s their tutorial on the Move/Resize Partition feature.
If this small guide helps you, tweet me @scojjac.