Since Windows does not offer the possibility to re-size in-use partitions you will need to use a 3rd party application designed for partition management. In this case you may use Acronis DiskDirector as it's a powerful tool with the ability to modify partitions right in the Windows environment.
Please download the trial version, install it and restart your computer in order for the program to gain exclusive privileges over your hard disk. Once you come back to desktop, start the application (a window will pop up asking you how you want to operate the application - please choose Manual). Once you will see your hard drive(s) simply select the partition you want to re-size and right click it then choose Resize. From the window that appears, drag the right slider to the left of how much your new partition you want to be. A new Unpartitioned Space will appear which you can use to create a new partition or merge it with another. Once you complete these operations, click the start Flag and wait for the process to finish. As the partition will be in use, the application will ask to restart the computer to gain exclusive access. Leave the computer to do its job and when it finishes, it will restart and you will see your newly resized partition in My Computer.
