Hi JayFeng,
Thank you for posting in Microsoft community!
What happens when you try to extend the partition?
How many drives do you have on your computer?
Do you have enough space in other drives?
Follow the steps on how to Resize a Partition.
a. Press Windows key + C on your keyboard to show the Charms bar.
b. Click on search.
c. Click settings.
d. Now type Partition in the search option.
e. Click on Create and format hard disk partitions.
f. In the Disk Management screen, just right-click on the partition that you want to shrink except c:/, and select “Shrink Volume” from the menu
g. In the Shrink dialog, you will want to enter the amount you want to shrink by, not the new size. For example, if you want to shrink your 50gb partition by roughly 10gb so that it will now be roughly 40gb, enter 10000 into the box.
h. Right-click on the partition that you want to shrink, and select “Extend Volume” from the menu.
i. Click ok and restart the computer.
Note that the extend partition feature only works with contiguous space.
Let us know if you are able to perform these steps. I will be glad to provide you with the additional options available that you can utilize to get the issue resolved.