Like Windows Vista, Windows 7 also has the option to change partition size, which means you can resize (extend or shrink) partitions with its built-in Disk Management (DM) (see picture below). You can change partition size, create, delete, format partitions by DM without the help of third party partition software. 
So, the third party partition plays an important role in this situation and it will be more convenient and safer. Here we will recommend you a good partition manager software to change partition size for your windows 7 Operating System - EASEUS Partition Master Professional Edition. It is comprehensive hard disk partition management tool and system partition optimization software, allowing you to create, Delete, Resize/Move, Copy, Merge, Splite or Format partition for Windows 2000/XP/Vista/Windows 7 both 32 bit and 64 bit. With user-friendly interface, it is such a powerful Windows 7 partition manager which can resize and move partitions without any data loss. All the operations can be previewed before you make the changes. Meanwhile, it can make up the limitations of Windows 7 in disk partitioning.
Except changing partition size under Windows environment, EASEUS Partition Master Professional Edition also enable you to create a bootable CD to manage the partitions.
Learn the step-by-step instructions of changing your partition size for windows 7 from here.
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