A hard disk partition: Is a defined storage space on a hard drive. Most operating systems allow users to divide a hard disk into multiple partitions, in effect making one physical hard disk into several smaller logical hard disks
1. In the Disk Management screen, just right-click on the partition that you want to shrink, and select “Shrink Volume” from the menu.
2. 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 100GB partition by roughly 20GB so that it will now be roughly 80GB, enter 20000 into the box:
Extend a Partition:
1. In the Disk Management screen, just right-click on the partition that you want to shrink, and select “Extend Volume” from the menu.
2. Then you can specify the amount that you want to increase the partition by. In this case, I’m going to extend it back to 100GB size that it was before.