What is Disk Management?
Disk Management is an extension of the Microsoft Management Console that allows full management of the disk-based Hardware recognized by Windows.
Disk Management can be used to partition drives, format drives, assign drive letters, and much more.
Windows 8 disk management
Right click My Computer
Storage -> Disk Management,
Built-in Disk Management has ability to shrink volume and extend volume then, your hard disk condition will show.
Then you need to right click on the partition which you want to shrink,
and choose "Shrink Volume",
then type how large the space you want to free up.
How to Create Simple Volume using the unallocated Space
Specify the amount of space
Assign a drive Letter
Format the volume and specify Volume Name
When there is some unallocated space next to the partition that you want to extend and right click the partition that you want to extend, choose "Extend Volume", and type the number of that unallocated space.
How to Extend a partition
Select Extend Volume
Select the size
and click next