Note: Backup Operator or Administrator is the minimum membership required to complete the actions below.
Caution: If the partition is a raw partition (that is, one without a file system) that contains data (such as a database file), shrinking the partition may destroy the data! For detailed information, open Disk Management, click Help on the menu bar, click Manage Basic Volumes, and then click Shrink a Basic Volume.

Shrink an existing partition to create new unallocated space, from which you can create a new partition:
Open the Start Menu, right-click on Computer, click Manage, expand Storage & select Disk Management.
Right-click a partition, select Shrink Volume, Enter the amount of space to shrink in MB & click Shrink.
Right-click the new unallocated space, click New simple volume, click Next, Enter the Simple volume size in MB, click Next, assign a drive letter, click Next, Enter the Volume label, click Next, and then click Finish.