Luckily, you have several options in your hand to follow. I will tell about two of the easiest and convenient ways you can try:
1. Using windows installation disk: If you have windows operating system installation disk around you, simply put the disc in your CD-Rom and restart your PC. This time boot your PC from the inserted Disc (Not from your hard drive). Actually you should go through the windows installation steps (But don't install fully) and when the Drive options come up, then delete all the drives and take off the disc and power off your PC forcibly (Maybe by unplugging it). That's it, now you will be with a fresh hard drive.
If you are unfamiliar with the Windows Installation, have a look at: The Ultimate Guide to Installing Windows 7. Trust me, it is as easy as 1-2-3.
2. Using a Bootable Partition Manager: This technique is also very simple and you may do some more advanced task through this method. You may use WinPE from Microsoft which offers similar task: WinPE: Create USB Bootable drive
Some third-party bootable Partition Manager are available in the market also which can be booted to a USB-drive and launch from there. Then you will have a nice GUI (Graphical User Interface) of an advanced Partition Manager. From there, you can simply achieve your task. You may look at this tool: IM-Magic Partition Resizer