This guide is to expand your Windows server disk that is still unused or unpartitioned.
Do this by clicking search: disk partitions then access "Create and format hard disk partitions".
In the Disk Management section, click on the drive you want to expand. For example, we want to expand Drive C to a disk partition that is still not set.
Below is a 2 GB disk that is still labeled as "Unallocated". We plan to merge these 2 GB "Unallocated" disks to drive C.
As such, right-click on Drive C and then "Extend Volume".
Then Next > Specify the number of MB we have to extend, in this case everything > Next > then Finish.
Congratulations, your "Unallocated" drive is now joined to Drive C.