Or do it the easy way, install VirtualBox and run Ubuntu as a virtual machine.
Unless you expect to be doing hardcore graphics or need access to exotic hardware, running Linux in a VM on windows it a thousand times easier and more flexible than dual booting. You can run Linux and windows apps at the same time, cut and paste or drag and drop data/files between them etc.
You could install ubuntu, kubuntu and mint all in the same time it'll take to install any one of those in a dual boot installation! And if you don;t want to use a distro any more, getting rid of an install is as easy as deleting a folder on your hardrive.
Another advantage is simple snapshot and backup, if, like me, you know how often Linux will eat itself when upgrading or installing third party software, you can do a fast snapshot and extremely quick restore to before the install to fix it.
All the while there being /zero/ chance for error causing you to lose access too or even accidentally format your current 7 partition.