Diskpart as the disk management tool of Windows, can help you manage your disks in a good state. You can use it to extend an existing volume/partition by following the next steps.
Step1. Open the command-line window by clicking Start, typing: cmd, or you can press “WIN+R” and type “cmd”. In the command prompt, type:diskpart, press Enter.
Then, it will run Diskpart session.
Step2. At the Diskpart prompt, type: list disk.
Then, all disks will be list at the prompt.
Step3.Then, type:select disk n
n means disk number. Here, you choose the disk which has the partition you want to extend.
Step4. Type: list partition
The partition(s) on the selected disk will be listed.
Step5.Then, you can select the partition which you want to extend. Type: select partition n
n is the partition number you want to extend. Please make sure there is unallocated space behind the partition you want to extend.
Step6. Type: extend size=n
n is the size in MB you want to add the partition.
Then, it will remind you that Diskpart successfully extended the volume. Here is a screen shot of the details.
When you’re finished, type exit to end up this progress.