DiskPart is a simple partition management system included with Windows Vista and 7. The program works through a command line interface similar to MS-Dos and lets you perform additional tasks not offered through the normal Disk Management interface. With DiskPart you can extend volumes to assimilate unallocated space. This makes it possible to merge with DiskPart by first freeing the space from a volume you no longer need and allocating it to the desired partition.
Copy any files located on the drive where you are going to free the space to an external hard drive, DVD, CD or other partition.
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Open the "Start" menu. Type "diskpart.exe," then click the link in the results pane.
Type "list volume" without the quotes at the command prompt.
Type "select volume (number)" without the quotes to select the volume you no longer need. Replace "(number)" with the number beside the desired volume as listed in the DiskPart window.
Type "delete volume" (without the quotes) to delete the selected volume and free up the space.
Type "select volume (number)" without the quotes to select the volume you want to merge with the free space. Replace "(number)" with the number beside the desired volume as listed in the DiskPart window previously.
Type "extend" without the quotes to merge all of the free space with the specified volume.