If you are unable to accomplish what you want using the built in app in Disk Management, you can use Easeus Partition Master (http://www.partition-tool.com/
Be sure to do a couple of things:
1) Using disk cleanup, delete all but the most current restore point
2) Empty the Temporary Internet Files Folder
3) Delete the contents of your Temp folder
4) Then empty the recycle bin
And of course, always backup all critical data before repartitioning the hd.